AETIOLOGICAL FACTORS IN CONGENITAL ABNORMALITIES

The problem of congenital abnormalities has been with us for many years. The surviving records of some of the oldest civilisations depict cases of congenital malformations. Achondroplasia is found in Egyptian paintings over 5,000 years old and the god Phtah revered at Memphis, the ancient capital of Egypt, is without doubt one of these cases. Club foot and cleft palate have also been detected in records and mummies of the Egyptian era. In other ancient civilisations, abnormalities have also been recorded. Prehistoric Peruvian pottery has been found to depict hare-lip and other malformations. Greek mythology included many instances of monsters which presumably have their origin in abnormalities. However, not all references to monsters by the Greeks were confined to mythology. Aristotle describes a monstrosity as contrary to the most usual course of nature. This is probably the earliest reference to someone thinking that congenital abnormalities are due to the unusual development of a normal process.

Sixteenth Edition. 52s. 6d., post 1s. 6d. T h e topic of obesity could provide material for a series of symposia. Personal prejudice has largely determ ined the aspects chosen for discussion here, and these are intended to dem onstrate features bearing on our understand ing o f the nature of this disorder, w hich, as is generally recognised, has such profound m edical and social im plications. A diposity itself is less of a problem than the sequelae and com plications which so com m only occur. T h e epidem iology o f obesity w ill not be dealt with now, bu t a m om ent's reflection on the m orbidity and m ortality associated with being overweight will suffice to emphasise the im portance of even a single exam ple such as diabetes m ellitus.

S U R G IC A L A N
In the studies to be discussed the necessity for a definition o f obesity naturally arises, but this need not be laboured. T ables relating height and weight, sex and age, arc readily available. T h ese tables usually provide a v e ra g e weights based on height. It m ight be argued that an average body w eight is less suitable than an ideal w eight as a basis for investigation and for planning treatm ent. T ables of average weights are based on actuarial analysis of previous experience, and these show a tendency for m ost people to put on w eight with advanc ing years. Such a concept appears to condone an increase in w eight that m ay indeed be harm ful. A t present it is im possible to assess the contribution m ade by coincident factors such as d im inishing physical activity to the disabili ties often attributed directly to obesity.
O th er standards have been proposed from tim e to tim e to distinguish the norm al from the obese, and these are usually based on m easurem ents or estim ates of the am ount of obese tissue in the individual. Som e o f these techniques arc as sim ple as m easuring the thick ness o f skin folds with a calliper in standard areas, while others are based on the volum e of distribution of deuterium oxide or tritiated water which will equilibrate with the total body water and from this the lean cell mass and thus by difference the am ount o f adipose tissue can be determ ined. W eigh in g under water w ill also provide an estim ate of body fat. T h e choice between these and other m ethods is not critical, however, for the purpose o f this paper. In studying obesity it is m ore profitable to select groups o f individuals w ho clearly transgress the bounds o f any norm al range, so that by any standard they arc clearly abnorm al.
W h e n confronted by an obese patient, and faced with the necessity o f advising treatm ent, two im m ediate problem s present them selves. Firstly, and as a m atter o f expediency, w hat advice should be offered? Secondly, w hy has the patient becom e obese? In seeking to rationalise the second question we m ay answer the first m ore effectively.
Fund am entally, it m ay be claim ed, the fat are overw eight because control of the balance between energy intake and ou tput is defective, and the balance remains positive too often for too long. From this prem ise it m ay be argued reasonably that the loss o f m e tabolic equilib rium could occur because the intake o f energy was in excess of needs, or alternatively, and even in addition, that the output o f energy was insufficient to deal with the load imposed on the intake side o f the equation. T h ese are really about the on ly assum ptions that can safely be m ade at present.
T h e contribution o f energy ou tput as a m echanism for m aintaining a steady w eight is difficult to study because o f the technical prob lem s involved, and particularly b ecause the in vestigation m ust be extended as far as possible in tim e in order to take account o f fluctuations that are constantly occurring. V ariations in the am ount of energy lost in the urine and stools can be discarded as factors of im portance in m ost cases. V ariations in the physical activity of the patient how ever certainly cannot be ig nored. E ven when it has been shown that the obese exert themselves less than those who remain thin, the problem remains w hether this econom y o f effort is cause or effect. O nly prospective studies would provide an adequate answer to this question and such an undertak ing m ay be well nigh im possible. Several workers, notably Stunkard, a psychiatrist in Philadelphia (C h irico and Stunkard, 1 960) and M ayer (Johnson, Burke and M ayer, 1956) in the D epartm ent of Public H ealth in Boston, have shown that on average the obese exert them selves less than do their m ore slender controls. T h is applies in children as well as in adults, and appears to affect girls m ore than boys. It m ay be noted however that the fat patient does m ore work than the lean in m ov ing the same distance, for the m ost obvious of reasons, nam ely that the bulk to be m oved is greater.
T h u s the conclusion stands that m any fat people spend less energy on kinetics than those who are thin, and they apparently fail to restrict their energy intake appropriately, and there fore becom e or remain obese. Fo r 50 years or m ore, suggestions have been m ade that the norm al individual has a m eta bolic " bypass" denied to the obese, for burning off surplus energy, and that for this reason the fat man w ho eats m ore than his energy output would require w ill accum ulate adipose tissue, while the thin man w ith his " bypass" remains thin in spite of eating m ore than is necessary to m eet his strict requirem ents. T h is postu lated m echanism was described as " luxus konsum ption" by G ra fe (19 3 3) but it has never really been dem onstrated with conviction. In deed m ore evidence has been adduced against it than in its favour.
T w o further aspects o f the ou tput side of the energy equation should be m entioned here. T h e first of these is exem plified by a group of seven grossly obese patients w ho were studied m ost rigorously under hospital conditions, but in a general ward. T h e ir diets provided between 370 and 550 kcal. daily only and by encouraging them to take exercise until they were walking as m uch as ten m iles daily, these patients were able to dissipate sufficient energy to achieve negative energy balances to the ex tent o f 2500-3000 kcal. daily. As m ight be predicted they all lost very substantial am ounts of w eight in periods o f six weeks study, the losses ranging b e tw ee n 13.4 and 17.3 kg. T h is o f course represents rather an unusual state o f affairs and w ou ld n o t n orm ally b e p racticable or perhaps advisable exce p t u n der strict super vision. O n ly th e obese w h o rem ain m e ch a n i ca lly in ta ct arc ca p a b le o f this degree o f a ctiv ity, b u t it serves to show w h at can b e achieved in this w ay.
T h e secon d a sp ect con cerns th e e ffec t o f exercise on a p p etite . T h e am o u n t o f exercise o n e takes w ill a ffect th e d e b it side o f the energy equ atio n , w h ile th e a p p etite w ill b e all im p o rtan t in d eterm in in g th e energy credit, assum ing th at free access to fo od is available. M a y er and his colleagu es (1954) carried o u t exp erim en ts using rats in cages e qu ip p ed w ith treadm ills so th at th e anim als w ere exercised daily fo r variable periods. W it h free access to fo o d , over a w id e range o f energy exp en d itu re, the anim als m atch ed th eir in take o f calories against th eir energy o u tp u t in such a w ay that th ey n eith er gain ed n or lost w eigh t. O n ly at e ith er extrem e o f p hysical a ctiv ity did this n icely balan ced m echanism show signs of breaking d ow n; at o n e end b ecause o f exhaus tion from overw ork. A t th e o th er end, and in fin itely m ore im p o rtan t fo r our u n derstan d in g o f o besity, w h en th e an im als' o p p o rtu n i ties fo r exercise w ere restricted, th eir food 15. co n su m p tio n rose ab ove th eir requirem ents, and as m ig h t b e e xp ected , th e ir w eig h t began to increase.
T h e im p licatio n is clear, n am ely th at energy in take w ill m atch the o u tp u t, p ro vid ed th e am o u n t o f p hysical exercise taken docs n o t fall b e lo w a certain m in im u m .
S o m e o f th e o th er factors bearing on th e rate and a m o u n t o f w eigh t loss o ccurrin g on red u c ing diets are illustrated b y th e case o f C h ristin e E . (Figs. 1 and 2). T h is p atien t was w eigh ed daily for a period o f som e 17 m o n th s, w h ile she was o n a d iet usually p ro vid in g app roxi m a tely 400 kcal. daily: occasional changes were m ade fo r special purposes. It m ay be added th a t in sp ite o f th e effort and exp en se in vo lved in supervisin g her d ie t and activities w h ile her w eig h t was reduced to less than h a lf h er in itial w eigh t, she has sin ce regained alm ost her original w eig h t and has n ow b e co m e a diabetic. B efo re th e end o f th e study, b ecause o f per sistent sup pu ration , it b e cam e n ecessary to excise h er u m b ilicu s, and this was rem oved alon g w ith a layer o f fat w eigh in g app roxi m a tely 12 lbs. D u rin g th e tim e covered b y F ig . 1 h er w eigh t was reduced from 156 kg. (344 lbs. or 24½ stones) to 76 kg. (168 lbs. or 12 stones). Such a fall is equ ivalen t to an average daily loss o f   Fig. 1 represent intervals o f one week. It w ill be noted that the fall in w eight tends to be step wise, and indeed at one stage fo r a period last ing several weeks she failed to lose any w eight at all, although adhering to the usual regimen. I n spite o f fluctuations of this type however, the overall loss o f w eight was steady through out. F o r a phase o f 8 m onths approxim ately, records were kept o f her m enstrual periods, and it will be seen again that abou t the tim e of onset o f her period, a sharp rise in w eight usually occurred, subsiding again thereafter with an appropriate increm ent in w eight loss, to resume the steady decline.
In Fig. 2 the daily w eight changes are shown that occurred in the interval follow ing her adm ission to hospital. T h e striking alterations in the rate of loss o f weight m ay easily be seen. From the point of view o f obese patients taking strict reducing diets, it is m ost im portant that they should be told w hat they m ay anticipate when dieting conscientiously.
Unless this is done they becom e disillusioned when the rapid initial loss of w eight o f the type illustrated in Fig. 2 fails to continue, and thereafter abandon the very real effort involved in adhering to a regimen likely to produce consistent results. E ven m ore discouraging are the phases o f water retention also illustrated, when not only is loss o f w eight not continuing but gains in w eight are occurring, som etim es for several days in succession. Phases o f this type m ay persist for 10 -14 days or m ore, and unless the patient is constantly rem inded that this failure to lose w eight is tem porary only, that it is relatively com m on and w ill be succeeded by a com pen sating period with an increased rate o f weight loss, only the stupid or unnaturally stoical patient is likely to continue with dietary re strictions.
T h e m echanism responsible for the water retention accounting in turn for these rather anom alous changes in w eight has not yet been identified.
Studies by R ussell (1962) on sodium an d water excretion by obese patients on reducing diets strongly suggest that the surplus water accum ulated in the circum stances described is aecom panied by sufficient sodium to keep the additional water retained isotonic with extracellular fluid: from tim e to tim e the excess o f both is released and excreted. T h ere are grounds for suggesting that som ething sim ilar m ay happen when m ore generous diets providing up to 1000 kcal. daily are in use. In these circum stances, feeding a high carbo hydrate diet enhances water retention, a high fat intake on the other hand w ill prom ote a m ore rapid rate o f loss o f w eight for a few days, until a new equilibrium has been estab lished, and w eight loss w ill then continue predictably, depending on the energy balance.
Studies undertaken in a num ber o f centres bearing on the w eight reducing properties of a variety o f diets would indicate that when adhered to strictly, and excluding short term differences due to variations in water balance, the ultim ate rate o f loss o f w eight depends upon the caloric content o f the diet, and not upon the form in which these calories arc taken.
It should be added that w hile the energy content o f food is all im portant in m aintaining w eight at a constant level, the relative content of carbohydrate, protein and fat in the food eaten are probably of m inor im portance except to the extent that they affect the palatability of food and therefore the appetite o f the patient. In the longer term , however, the reverse w ould be true when the patient or subject has freedom o f access to food. T h e satiety value or appetite suppressing properties o f food m ust be o f the greatest im portance in determ ining when a person with free access to food w ill stop eating. O ur ignorance in this regard m ust largely be attributable to the form idable problem of dem onstrating in man w hat it is that stops him eating. W e know that in anim als hypothalam ic centres for eating and for satiety can be dem onstrated, and that exercise and tem perature,solitary confinem ent or group feeding, restricted periods of feeding or continuous access to food can all affect the issue quite profoundly.
T h e heat conserving properties o f a layer of subcutaneous fat and the effect on body tem perature was studied recently b y Q uaade (1963) in C openhagen. H e m easured the skin tem perature 011 the surface and the tem perature deep to the abdom inal layer of fat in groups o f obese, norm al and thin individuals, and showed that although the abdom inal tem pera ture in the fat man is slightly higher than in the thin, the skin tem perature is lower in the fat. T h e re are several possible explanations for these differences, but one reasonable interpictation would be that a heavier layer of surface fat is a m ore effective insulation against heat loss than a lighter covering of this type. Such a factor m ight contribute to the difficulty som e patients evidently have in dissipating surplus energy.
T h ere arc relatively few studies available of protein m etabolism in the obese and such as there are indicate that it m ay be norm al. T h is conclusion, however, should be accepted with reserve for the present. O ur own investigations suggest that obese patients lose little protein when taking severely restricted diets.
T h e obese also show an unusual resistance to the developm ent of ketosis: unusual in the sense that under dietary conditions and condi tions o f exercise, where the lean can be ex pected to excrete relatively large quantities of ketone bodies, the obese fail to do so. T h is too is characteristic o f the m aturity onset insulin resistant adult diabetic who is usually obese, but the protective factor possibly com mon to these two im portant conditions and responsible for their relative im m unity to ketosis remains to be shown.
O ne popular form o f practical therapeutics for the control of obesity is the use o f so-called appetite suppressants. In a society with access to unlim ited quantities of food, the problem for m any is when to stop eating. T h e clinical response to dietary restrictions is disappointing indeed, and there is a pressing need for som e m ethod of controlling appetite that does not depend only on the p atient's ability to exercise restraint at the tabic. T h e com m ercial possi bilities for appetite suppressive drugs have not been wasted on the m anufacturers, and there arc now 25 or m ore such preparations available in this country. M o st of these drugs are ep h edrine derivatives. Som e years ago m y col leagues and I attem pted to assess the value of two o f these drugs in the m anagem ent of obesity (H ampson et al., 1 960). D exam pheta m ine is widely used for this and other purposes, and it seemed a useful standard for com parison w ith a further drug on behalf of which at that tim e strong claims were being m ade for its efficacy as an appetite suppressant, nam ely phenm etrazine. Both were com pared against an inert placebo m ade o f chalk.
T h is clinical trial was arranged with out patients attending for dietary advice and they were all prescribed diets of approxim ately 1000 kcal. daily. T h e y were seen at intervals o f one week, and were given each treatm ent in turn for 3 periods each of 6 successive weeks duration, m aking 18 weeks in all. T h e order o f adm inistration of the 3 drugs was random ised, so as to elim inate as far as possible bias in favour of or against a regime because it cam e earlier or later in the period o f study. A nalysis showed that both the drugs were som ewhat m ore effective than the control tab lets, but that when the results were rearranged and com pared, irrespective o f the drug but rather between the order o f the 3 periods of treatm ent, m uch m ore was achieved in terms o f w eight reduction in the first period o f 6 weeks, than in either o f the two succeeding.
From this has emerged the view that this g roup o f drugs m ay have som e little help to offer, but only as a tem porary expedient. It is widely recognised that they m ust be regarded as drugs of addiction, and indeed our psychi atrist colleagues as well as others would be glad to see their use in the treatm ent o f obesity restricted or abolished altogether. A norectic drugs are never a substitute for the discipline of dieting, and the m arginal benefits they have to offer seldom ju stify their use.
Practising doctors are constantly preoccupied with the necessity for weight reduction and the difficulties surrounding this process. Prophy laxis is the essence of good treatm ent, and this applies to overnutrition just as it docs to so m any other disorders. A lthough so m uch attention has been paid to the process o f reduc ing weight, very little has been done to study the m echanism o f gaining w eight in the obese. Several years ago D r. Passmore and his col leagues (19 55) carried out energy balance studies on a group of thin young men who were overfed to capacity for a relatively brief period. In 1962 we (Passmore, Strong, Sw in dells and el D in , 1963) did the same for a pair of overweight young women who after a period of equilibration ate as m uch food as they could tolerate. In the course of 9 days overfeeding, largely with carbohydrate, they gained alm ost 3 kg. in weight, bu t in 6 days afterwards of alm ost com plete starvation, they not only lost the 3 kg. gained, but also alm ost 3 kg. further as well.
W h en the findings in the fat young women were com pared with the thin young m en, re markable differences were seen. T h ese studies suggest that there is som e substance in the frequent com plaints o f the obese about what they regard as a form o f biological injustice and what is sceptically disregarded by their physi cians, nam ely that when taking the same am ount of food as their thinner fellows, they gain weight, while the lean remain so. For a given excess of calories, the fat girls gained w eight m uch m ore dram atically than the thin m en, and indeed for com parable gains of weight, the excess of calories required by the thin men was m ore than twice that for the girls. F o r a gain of 2.5 kg. in weight, 20,000 kcal. each was needed by the thin m en, as com pared w ith 10,000 and 6,500 respectively by the two fat girls.
T h is procedure o f com paring the fat with the lean has led to studies in other aspects of m etabolism as w ell, in cludin g steroid horm one m etabolism . In recent years m any reports have appeared, m ainly concerned w ith adreno cortical function, and usually show ing that the excretion o f 17-hydroxycorticosteroids was g reater in the fat than in the lean. A nalysis of this data com m only indicates that the higher findings recorded are associated w ith, and pos sibly accounted for, b y the greater bulk o f the obese patient. T h e re is n o doubt that som e fat people go through a phase when their adrenocortical function is so vigorous as to create serious doubts regarding their clinical status, in the sense that they m ay be regarded as suffering from C u sh in g's syndrom e. O ne further aspect o f our eating habits should be m entioned. S T U N K A R D has described w hat h e calls the " night-eating synd rom e" , im plying that this group o f obese patients cats little during the day, but in the evening and at night consum es large quantities of food. T h is perhaps is an extrem e exam ple o f a com m on h abit o f eating little or nothing of energy value at breakfast or lunch, bu t then taking a large evening m eal.
H ollifield and Parson (1962) have studied a com parable regim en in rats. O ne of two sim ilar groups o f rats was allowed free access to food at all times, while the other group was allowed to feed for two hours daily only. A fter a brief period when the " 2 hour feeders" lost som e weight, they rapidly caught up w ith and overtook their controls who had free and con stant access to food, as is usual with laboratory rats. T h e different rates o f gain in w eight were not accounted for by differences in food intake, and other studies o f fat m etabolism were thought to provide a tentative explanation. So far as is known the activity o f the anim als was not controlled, and one possibility would seem to be that the " 2 hour feeders" soon learned when it w ould be to their advantage to hunt for food, and that for the rest o f their tim e they conserved their energy in rest or sleep.
Studies of the m etabolism of labelled acetate by these anim als showed that the " 2 hour feeders" in the course o f seven days increased enorm ously their capacity to store the acetate as adipose tissue. T h e suggestion is therefore that adaptation to this unusual type o f feeding regimen radically altered the m etabolism of the anim als, so that they developed w hat m ay be described as a " storage phase" o f fat m eta bolism .
T h ese and m any other m etabolic differences that are em erging to distinguish the fat from the lean offer the prospect that out o f these investigations m ay arise better m ethods of m anaging disordered w eight control and so reduce an im portant source of m orbidity and m ortality in the better fed countries o f the world.
T h e wonder o f it is perhaps not so m uch that som e becom e obese, but rather that this fate overtakes so relatively few.

AETIOLOGICAL FACTORS IN CONGENITAL ABNORMALITIES
By ALEXANDER M. DAVIDSON, B.Sc.

Based on a Dissertation read before the Royal Medical Society
on Friday, February 14th, 1 964

I. I N T R O D U C T I O N
T h e problem o f congenital abnorm alities has been with us for m any years. T h e surviving records of som e o f the oldest civilisations depict cases o f congenital m alform ations. A chondro plasia is found in Egyptian paintings over 5,000 years old and the god Phtah revered at M em p his, the ancient capital of E gyp t, is w ith ou t doubt one o f these cases. C lu b foot and cleft palate have also been detected in records and m um m ies of the Egyptian era.
In other ancient civilisations, abnorm alities have also been recorded. Prehistoric Peruvian pottery has been found to depict hare-lip and other m alform ations. G reek m ythology in cluded m any instances o f m onsters which pre sum ably have their origin in abnorm alities. H owever, not all references to m onsters by the G reeks were confined to m ythology. A ristotle describes a m onstrosity as contrary to the m ost usual course o f nature. T h is is probably the earliest reference to som eone thinking that congenital abnorm alities are due to the unusual developm ent o f a norm al process.
A lthough painting and sculptures o f abnor m alities exist from som e o f the earliest civili sations it is not until fairly recent times that any effort has been m ade to determ ine the aetiology o f such defects. In the M id d le A ges the birth o f a congenitally defective child was viewed with superstition and fear. E ven physicians were inclined to ascribe such events to the supernatural and m ystical cause. T h e fam ous French surgeon A m broise Pare tabu lated the causes of m onstrosity beginning with G o d and ending with the D evil. T h is list is far from being ridiculous, and m any of his ideas have a firm foundation. T h e causes he gives fall into three large categories-religion and superstition; environm ental factors; and here ditary. Although we w ould generally agree that G o d and the D evil have no direct inter vention, the other two reasons still hold.
It was not until the 18 th century that som e o f our present day ideas about m alform ations had their scientific foundations. T h ere began the collection and exam ination o f embryos. T h e norm al developm ent of em bryo and foetus was investigated and the deviation from norm al noted. From such studies M ick el was able to show that som e abnorm alities arc not due to random growth but persistence o f som e stage of norm al em bryonic developm ent. It was not long before m any theories arose explaining all abnorm alities on this basis. T h is prom pted investigations into factors which could in fluence the development of an embryo and thus the era of experimental embryology began. Since the early experiments, work has increased in amount and in variety.

II. A ETIO LOGY
T h e causation of congenital malformations can fall into two main groups: Intrinsic factors and Extrinsic factors. T h e intrinsic factors arc genetically determined anomalies either due to alteration of the gene or the chromosome. T h e extrinsic factors include all agents which can have an effect on the normally developing child. This list includes such factors as radi ation, drugs, mechanical disorders of the womb producing pressure symptoms, infections, diet ary deficiencies, hormonal imbalance and environmental factors. However, although this list is impressive by its length, it is important to realise that the aetiology of most malforma tions is not clearly understood. Even in cases where a causal agent can be detected it is still obscure how many of these factors produce their effect.
Alterations in the gene can lead to a wide variety of conditions. Hereditary malforma tions of the digits arc fairly common and can in some cases be traced back through many generations. Phalangeal synostosis can be traced back for fifteen generations in the family tree of the Earl of Shrewsbury. In many in stances a genetic defect may not produce such a simple picture. In arachnodactyly due to a dominant gene, there is a multitude of malfor mations both ectodermal and mesodermal. There arc long hands with spidery fingers, spinal anomalies arc common, including hemivertebrae, the eyes are often affected in numer ous ways and heart anomalies are common.
T h e fact that there are multiple anomalies, some of which may occur alone, lead many people to think that such a syndrome was due, not to one gene, but multiple gene abnormali ties. T h e present day feeling is that the gene is no observer of germ layers and that there is almost no limit to the effects that they can produce. However, it may be that with further research a syndrome with multiple defects will be traced to a single enzyme defect in a similar way to the recent elucidation of phenylke tonuria. Alternately the defect may be in an organiser which would be much more difficult to trace and characterise.

Genetic and Chromosomal
In the case of the chromosome there are two main types of aberrations, either anomalies of number or translocation of part of the chromosome.
Probably the best known anomaly of number is trisomy 21 associated with mongalism. There is an interesting malformation of the hands in such patients -a horizontal palmar crease and char acteristic finger prints arc seen. This was probably the first congenital condition con nected to a chromosomal defect. Other trisomy conditions have since been recognised. In trisomy 17-18 there is a flexion deformity of the fingers, mental retardation, hypoplasia of the mandible, small mouth, low set ears and ventricular septal defect. Another recognised condition is trisomy 1 3-15 in which polydactyly -frequently quadrilateral, mental retardation and eye defects are seen. How the extra chromosome in such cases produces these mani festations is pure conjecture.

EXTRIN SIC FACTORS
Radiation A t the present time there are three main means whereby we can be exposed to ionizing radiation; during therapy, from environmental background and by accidents.
Radiotherapy may play an important part in the treatment of disease. As it is normally administered by competent people, the hazard from this source is considerably reduced. In many cases, however, the difference between adequate and harmful dose is small and diffi cult to judge. Changing the dose of radiation by as little as 10 % may render the dose lethal, a point seldom considered by people not used to dealing with therapeutic agents having this fine borderline between curvative and lethal doses.
T h e e n v iro n m e n ta l rad iation has alw ays been p re se n t b u t re c e n tly d u e to su ch d evices as d ia g n o stic X -rays, th e e xp lo sio n o f test It is th e re fo re n ecessary w ith regard to rad iatio n to en su re th at w ork ers an d p a tie n ts receive o n ly th e m in im u m a m o u n t o f rad iation a n d th a t p re g n a n t w o m e n receive rad iation o n ly a fte r ca re fu l c o n sid e ratio n .

Infections
Follow in g the discovery of bacteria it was thought that congenital m alform ations were due to bacterial infection. It was known that syphilis would cause foetal death with subsequent abortion and so syphilis was nam ed as the prim e cause o f m alform a tions. H owever, with the introduction of therapy against syphilis and the subsequent fall in its incidence not follow ed by a corresponding fall in m alform ations investigations turned in other directions. As with so m any other cases, investigators were looking for one cause of m alform ation. W e now know that this con cept is false and that bacteria and viruses do have a part to play in the aetiology of abnorm alities.
It is well known that rubella in the first trim ester o f pregnancy m ay produce m alform a tions. T h e m echanism w hereby the rubella virus produces its lesion is unknown but it has been suggested that it is due to the localisation o f the virus in the developing em bryonic cells causing their death. O th er theories are that the virus initiates a m etabolic defect or that it constricts blood vessels producing anoxia. H owever, as with m ost conditions which have a m ultiplicity of theories as to aetiology little is really known as to the m ode o f action o f the rubella virus.

Dietary Deficiencies
A lthough m alform ations can be produced in anim als fed on diets lacking in som e constituents these m alform ations are not found in hum ans. T h e only dietary factor of any proved significance is iodine. E n d em ic cretinism occurs in areas where endem ic goitre is com m on. T h e child is born with an enlarged thyroid and shows a generalised lesion of bone, the growth of which is severely im paired. T h e bones are sm aller and shorter than norm al due to a defect in endochondral and intra-m em branous ossifica tion. A n interesting feature is the presence o f deaf m utism in m any o f the affected cases.
H orm ones D isturbances in horm ones in the m other have been regarded as causes of congenital anom alies but this is not based on sound evidence. A b o u t the only d efect due to this cause has been the appearance o f m asculinised genitalia o f som e fem ale children born to m others who received synthetic progeste rones for threatened abortion.

II I. S U M M A R Y
In this article only sonic of the know n causes of congenital m alform ations are discussed. T h e aetiology of m any conditions has still to be worked out and with further elucidation the door m ay be opened towards prevention of m any o f these crippling conditions.
T h e R oyal M ed ical Society w ill leave its present premises for tem porary ones, with the hope o f eventually m oving into new accom m o dation in the projected ' Island S ite ' near the M cE w an H all.
W o m en are allowed full m em bership. A t first Private Business tim e is spent on issues o f pre-clinical interest, instead of Society m atters. A t such a tim e it is justifiable perhaps, to speculate on the future of the Society, to conjure up visions of its future. A nightm are and a dream emerge.
T h e nightm are is a fleeting one. A venerable institution, som e 228 years old, its quarters surrendered, parts with its library -the old dusty tom es so m uch a part o f the societyand m oves into 'tem porary' premises. W ith n o vision of its role in the student w orld of the 20th century, com forted by its past glories, it prefers quiet com fort as a sm all 'M edical C lu b '. It speaks with a sm all voice because student support is lim ited. T h e cries for help and for new premises grow weaker and weaker. T h e y die aw ay eventually. N oth in g remains.
B u t the dream is insistent. T h e Society, leaving its premises, also leaves its lethargy behind. It is com posed o f students who visualise for the Society a central role in m edical student life. Because of its activity and drive its tem porary accom m odation gives place to facilities in the Island Site w hich form a fram ework for Society activities. A M eetin g H all, a warm Library with journals and current text-books, a lounge where students can relax, drink coffee and talk, arc continually in use. E ru d ite guest speakers learnedly address the Society, and the society m em bers present dissertations. Private m eetings arc the hub of the Society, with lively, inform ative discussion, with films, debates, and clinical presentations. Freshers visiting for the first tim e arc drawn into the discussion. It is a Society which com bines its historic tradition of quality with vigour and enthusiasm .
O ne wonders w hether the Society will be a dream or a nightm are.

HOUSE-JOBS IN SEARCH OF CLARITY
T h e scram ble for house-jobs in Edinbu rgh is a continuous one, spread, as it is, over the last two years o f the m edical course. As there is no official statem ent about obtaining these posts, inform ation is handed down from year to year in a haphazard fashion. Som e posts are offered early, before final year and som e times before fifth year. O n other units, house m en m ay be selected after finals.
T h e present system, if 'system ' is the correct word for w hat occurs each year, has inherent f rustrations for 'ch ie f' and student alike. T h e consultant in charge o f one o f the less fashion able units m ay m ake his selection early to ensure that the posts are filled. B u t he m ay later m eet students in senior cliniques, in clerk ships and in locum s who he m ay prefer to have as house-men. Furtherm ore, the student accepting a post early m ay, if offered w hat he considers a m ore preferable post, turn down the earlier offer. T h e annoyance of the 'ch ie f' is understandable particularly if he has refused desirable applicants because the post was filled.
A noth er consequence of the present system is that students w ho are not given jobs early autom atically apply for the still vacant jobs. H ence there are long lists of applicants in the final term , often for jobs already prom ised.
T h e c hief has always had, quite correctly, com plete responsibility for selecting his house m en. B u t surely his task can be m ade sim pler, and the students position clarified. T h e follow ing suggestions m ay bear consideration, discus sion, and, who knows, introduction.
1) A fixed final date for applications, e.g. 1 st M arch . Students are then clear when to apply, and m any 'ch iefs' have had w ider contact with students before final selection.
2) A date by which selections should be m ade, perhaps a fortnight later.
3) Successful applicants arc then inform ed, and arc required to accept or refuse w ithin a week. T h o se having been offered m ore than one post, will accept the post o f choice. Successful applicants w ill also im m ediately w ithdraw other applications. 4) T h e position would then be that a large percentage o f applicants w ill have been offered and w ill have accepted posts. Posts w hich have not been accepted can then be offered to re m aining applicants.
Such an arrangem ent does not increase the work o f the 'ch ie f' in selecting house-men, nor docs it detract from his freedom to select his house-men. H e m ay still 'prom ise' jobs if he wish. T h e only alteration is in the tim e of selection. Fo r those who select their house-men early, the frustration of late refusals o f posts is elim inated, and their choice o f house-men increased. F o r those who select their house men late there is little alteration. C ertainly it will bring clarity to the students who, per plexed by the w ide range o f times of selection, wonder w hether they should m ake early appli cations, before the experience of a variety of cliniques, before further clerkships and locums. Wed.

SYLLABUS
10 Annual E xtraordinary General Meet ing.

P R I V A T E M E E T I N G S
T h e Private M eetings of the Society provide a varied program m e of T alks, discussions, case presentations, and debates. First Private M e e t ings, held at 7 p.m ., are orientated towards pre-clinical students, and Second Private M eetings are orientated towards the clinical student.

I N T R O D U C T I O N
Pain is one of the m any facets o f our education w here we learn the basic facts and theories in the early years o f our m edical course only to forget m uch o f our learning by the tim e we are qualified and in practice. In the clinical years we tend too often to learn sites and types of pain by m em ory, each type associ ated with one certain disease: all too rarely do we stop and ask ourselves the question " W h y ? " and attem p t to reconsider the basic theories in the ligh t o f the present evidence. It is a healthy attitude to challenge current teaching now and then in order to see how well it m atches up to current practice and current evidence.
Pain is a prom inent sym p ton in m any diseases: its relief is often a perplexing problem to the doctor but paradoxically it can play a useful part in the construction o f an exact diagnosis. A history which is well related by the patient and intelligently interpreted by the doctor is m ore im portant to the diagnosis and hence to the treatm ent than all the exam ina tions, clinical or laboratory, w hich later follow . Indeed the history usually dictates the subse quent steps. U n fortun ately the viscera o f the body are not endowed with the sam e sensory p recision as the skin and thus visce ral pain is m ore difficult to describe and to locate than cutaneous pain. Progress in the understanding of pain has n o t been easy-not for w ant of interest but rather because o f the difficulties concerned with any form o f experim entation. It cannot be repeated too often that any theories offered m ust fit the facts. In record ing the clinical facts o f each case great care m ust be exercised to keep the facts quite distinct from the conclusions drawn from them -D arw in in the D escen t o f M an in 1889 warned us: " False facts are h ighly injurious to the p rogress o f science for they often endure long; but false views, if supported by som e evidence do little harm , for everyone takes a salutary pleasure in proving their falseness." D arw in 's w arning is all too often ignored and theories and deductions becom e taught as facts. T h u s it is not uncom m on to find C a p p 's work on the sen sitivity of the peritoneum taught as an established fact rather than as a deduction; yet n o less an auth ority than M ackenzie has claim ed that the peritoneum is not itself sensitive to cutting, scratching, etc. Sim ilarly we are used to describing the pain o f passage of a renal calculus down the ureter as " renal co lic" and tend thereby to im ply the rh ythm ic w axing and w aning o f pain in associ ation with peristalsis such as happens in in testinal obstruction: having learned the term "ren al co lic" it is too easy to forget the true fact that the pain o f renal calculus is not colic in that sense at all. D r. French o f this m edical school has drawn our attention to this danger and a few m inutes spent by the bed-side of such a p atient w ill convince the student o f the truth o f this. A n attack of " renal colic" w ill impress even the sceptic.
T h eories o f the m echanism s o f visceral pain have to be fairly broad in as m uch as they m ust explain not only the every day occurrence bu t also the unusual: this can be illustrated by the follow ing e x am ple:- T h u s th e pa in o f co ro n a ry th ro m b o sis is located d iffu s e ly by th e p a tie n t in th e praec o rd iu m , th e neck, th e a rm and even th e ha nd : a ffe re n t fibres are e n te rin g th e sp in a l cord at a ll these va ryin g levels o f segm ental d is trib u tio n and th e pa in is associated w ith these a p p ro p ria te segm ents on rea ching conscious ness. In som e instances pa in is in te rp re te d by the b ra in as o rig in a tin g a t a considerable distance fro m th e site o f s tim u la tio n -an ex a m p le o f th is has already been given. Such a p p a re n t errors in lo c a lis a tio n have been desig nated as " referred p a in " . John H u n te r first conceived th e idea o f pain reference w h en h e observed th a t diseases o f th e liv e r c o u ld cause pa in referred to th e sho ulder. Since the n m an y theories have been advanced and m an y heated arg um e nts have occurred on th is sub je ct. I n 1920 M a k e n z ie suggested th a t visceral a ffe re n t s tim u li set up an ir rita b le focus w ith in th e spina l cord and in tu rn th is so d istu rb e d th e so m a tic secondary neurones th a t th e ir th re sh o ld was low ered and thu s cutaneous im pulses, p re vio u sly su b -th re sh o ld , n o w reached consciousness. C o h e n (1947) m ade th is basic reasoning m o re elegant b y p o s tu la tin g th a t referred pa in is due to th e s u m m a tio n o f im pulses fro m b o th th e p e rip h e ry (fo r exam ple th e skin ) and fro m a viscus to g e th e r exceeding th e th re s h o ld fo r pa in . I t sh o u ld be stressed th a t th is means th a t im pulses fro m e ith e r source i f stro n g en ou gh , o r fro m b o th sources to g e th e r, can cause pa in b u t such pa in w ill be in te rp re te d as located in th e area o f skin c o n cerned. W it h th is th e o ry th e reference o f pa in to a site n o lo n g e r present (e.g. an a m p u ta te d a rm ) can be exp la ine d.
V isce ra l tenderness, o r pa in in d u ce d by pressure is an acccp ted fact.
Morley (1 9 31) considered th a t i t was due to th e " sensitive p a rie ta l p e rito n e u m " c o m in g in to c o n ta c t w ith th e causative le sio n -th u s in a p p e n d ic itis th e secondary pa in and th e tenderness were in the right iliac fossa where the inflam ed appendix lay (Fig. 1). Kinsella (1948) has offered another theory which perhaps explains m ore clinical facts than does M o rley 's. In K in sella's theory the pain from an organ such as the appendix travels along the sym pathetic afferents and is felt in the m id-abdom en since the gut has bilateral innervation. T h e pain im pulses probably originate in the rising tissue pressure of the inflam ed organ. M ovem en ts o f overlying tissues such as m uscles, or pressure o f an exam ining hand w ill increase the tissue pressure and aggravate the pain. T h e sensorium is well aware of the site of such an exam ining hand, etc., since the skin has also been stim ulated and co n seq u en tly locates the pathology there. T h is is w hat K in sella has termed " borrow ing local signature" (Fig. 2).  or it m ay be apparently m isleading if the second stim ulus-the exam ining hand-is applied in the reference area of the pain, as shown in Figu re 4. It is of course the unwary clinician who is m isled rather than the facts which are m isleading but doctors arc not im m une to the desire to excuse their short com ings.   B row n (1949) has offered a useful rule for referred pain, stating that an organ w hich is displaced from its p rim itive em bryological position subsequently refers its pain to its o rigin al p o sitio n , e.g. d ia p h ra g m a tic pain m ay be referred to the sh o u ld e r in C 3 , 4, 5 area from w h ich m yo to n ie s the d iap h ragm was d e ve lo p e d alth o u g h su b se q u e n tly w id e ly sep ar ated from th o se segm en ts. skin segm en ts. S u ch a stu d y suggests th at w h en T 12 cu tan e o u s se g m e n t is s e n ti e n t, th ese p atie n ts have te sticu lar sensation also b u t refer th e pain resu ltin g fro m testicu lar co m p ressio n to th e groin or to th e area o f the d e e p in gu in al rin g even a lth o u g h th e skin over th at area is itse lf in sen sitive.

CLINICAL APPLICATION OF KNOWLEDGE ILLUSTRATED BY TESTICULAR PAIN
ii) H u n te r's a d v ice o f " try th e e x p e rim e n t" can b e taken . A scries o f vo lu n te e rs had th eir scro tu m s an aesth etised b y lo cal a n ae sth e tic. A n e e d le w as then passed th rou gh the a n a e sth e t ised skin in to the testis: th e vo lu n te e r fe lt n o pain from this m a n o e u vre p ro vid ed the n e e d le w as sharp.

TESTICULAR PRESSURE
iii) T h e third source of evidence is to be found in the best laboratory of all-clinical practice. Thus patients with testicular pathol ogy or vague lower abdominal pain can be studied in detail, their histories taken with patience and care, their relatives interviewed and their pathologies and clinical courses noted. Such a study again leaves little doubt that the site of the earliest discomfort or pain in a patient with testicular pathology is in the groin or lower Abdomen and only later is localised to the scrotum by the patient.
Patients have been seen with a wide variety of diseases of the testis (torsion, torsion of the hydatid of Morgagni, trauma, epididymoorchitis, tumour of testis, undescended testis, infarction of testis) and the collected evidence again led to the above conclusion as to the true site of the earliest pain.
It should however be noted that many of the patients referred to in (iii) above were unaware of the association of their vague lower abdom inal pain with the " later developing" testicular lesion: so often were their medical advisers. A clinical case may be quoted to illustrate such points:-A patient was admitted to hospital for aortography as investigation of his intermittent claudication; exactly 10 hours after the injec tion of dye into his aorta he summoned the house surgeon to complain of abdominal pain in the right iliac fossa. T h e doctor concerned could find n o abnormality on examination. Fifteen hours after injection the patient again summoned the house surgeon to point out that he now had pain in his scrotum when he touched or moved the part but not when he lay still. Examination of the X-ray plates showed that the injection had filled the right testicular artery completely: necrosis of the testis followed.
From the clinical evidence referred to there seems little doubt that the patient's first dis comfort or pain in such cases is in the region of the deep inguinal ring: this accords with Brown's law. A t a later stage in the disease p rocess the patient is enabled to localise his lesion to the scrotum cither by virtue of selfexamination or by pressure of his thighs rais ing testicular pressure still further, but in such circumstances he has really elicited scrotal tenderness, or as Kinsella put it, he has " bor rowed local signature" . T h e lesson to be learned is that early examination of the scrotum in cases of vague lower abdominal pain can elicit local tenderness of the testis at an early stage-a stage in fact when oper ative intervention could save a reasonable pro portion of twisted testes.

CLINICAL MISREPRESENTATIONS
I n 1923 M ackenzie wrote " In all your observations keep your facts distinct from your interpretation" and this advice is all too easily forgotten. T h e apparent logic of expecting to find pain located accurately to the site of the stimulus is so pressing to some clinicians that it can lead to frank misrepresentation of the facts. Thus on several occasions have house surgeons recorded in the case notes expressions such as " pain in the abdomen" or " pain in the groin" when admitting the patient to the ward at a time when the diagnosis was unknown: T heir better qualified but undoubtedly less exact seniors have subsequently recorded in the summary of the case (or letter to the family doctor) that the patient was admitted " with pain in the testis" -the causative lesion by this time being known to be in the testis.
It is a very easy step to manipulate the facts from the point of truth to what seems to have been the truth without there being any delib erate intent to deceive. Patients too may be confused by their apparently logical conclusions concerning their own diagnosis: the mother of one boy who lost his right testis after a torsion reflected how unfortunate her young son had been " in first having a threatened appendicitis for three days and then going and developing this trouble with his testicle" . (T h is boy had been observed at hom e for three days with abdom inal pain before localising his pathology to his testis.) T h e catheters were then clam ped fo r varying times ranging from 2 to 8 m inutes. 20 to 40 one m illilitre sam ple were collected autom atically in vials fixed into a m oving bar. T heoretically, clam ping the ureter produces a rapid pressure build up in the tubules until the back pressure equals that of the glom erular filtration pressure. A stationary colum n of fluid is then in contact with the tubular epithelium w hich perform s, in an exaggerated fashion, its norm al functions. W h en the clam p is released, the fluid is for cibly ejected. T h e first samples obtained are those from the distal tubules and the later ones from the proxim al tubules. T h e results showed that acidification, am m onia production and potassium-sodium exchange all reached peak values in the same samples, these being those from the distal tubules. Phosphate reabsorption occurred in the proxim al tubule sam ples and was in no way related to the acidification pro cess. A lthough this m ight appear conclusive there arc m any criticism s o f the m ethod. As samples were collected in air sm all p H changes could be missed. A lso, the pelvis o f the kidney acts as a m ixing cham ber, this effecting the later samples in particular. T h e m ethod therefore provides valuable qualitative infor m ation but care m ust be taken in interpretation of the results.

SUMMARY
O ne further technique has been used. U lrich and E igler (1958) managed to insert a polyethylene catheter into the collecting ducts o f hamsters. T h e y confirmed the long suspected fact that there is a large p H fall at this site.
T h e first indication that these do not provide the com plete answer cam e from E llin ger as early as 1940. H e observed colour changes of an indicator passing along the tubule. In both the frog and the rat he found that acidification occurred specifically in the distal tubule only during a m ild acidosis. If the urine was strongly acid then he found colour changes along the length o f the nephron.
O ne o f the m ost com plete scries o f micropuncture studies was perform ed by G ottsch alk, Lassiter and M ylle in 1 960. T h e fluid collect ed was scaled in the m icropipe ttes which also acted as m icroelectodes. T h e pH was deter m ined by potential changes in the fluid. A ll their equipm ent was equilibrated w ith air con taining C O 2 at 27 m m H g. C o llection s were obtained from non-diuretic anim als and from those in a state o f osm otic diuresis, both nor m ally and during an am m onium chloride acidosis. In all cases there was a progressive acidification along both sections o f the tubule. (F ig 1.) T h is is conclusive proof that, in rats at least, proxim al tubules can acid ify urine. B io chem ical analysis has shown that equal am ounts of carbonic anhydrase , the enzym e necessary for hydrogren ion exchange, arc present in both sites. O bviously this state o f know ledge is tar from satisfactory bu t it m ight be profitable to attem pt to sum m arise the m echanism s propos ed at this tim e. A b o u t 8 0 % o f the glom erular filtrate is reabsorbed in the proxim al tubules under w hat Sm ith called " obligatory reabsorp tion" . T h e evidence suggests that the bulk of the hydrogen ion exchange also occurs here.
T h e distal tubules are capable o f the sam e pro cesses and probably act as the fine adjustors of p H in the same way as they regulate the 'facultative reabsorption" o f water. T h e collect ing ducts can m ake very little contribution to overall sodium and bicarbonate reabsorption as the load presented is very sm all. L arge pH changes could occur with a relatively low hydrogen ion secretion rate.
H aving thus attem pted to localise the pro cesses in the occurring kidney the actual m ode of transport o f ions by the tubular cells m ust be discussed. T h e first recorded experim ents on active transport in the kidney cam e from W ilb ran d t in 1 9 38. T h ese he perform ed on N ecturus which is an anim al having conveni ently large nephrons w ith long straight proxi m al tubules.
H e measured potential differ ences between the surface o f the kidney and the lum en o f the tubules using for elcctrodes m icropipettes sim ilar to those used by Richards. H e obtained " transtubular p otential" values of up to -12 m V , negative inside the lum en. T h is he interpreted as being due to different ion perm eabilities on the two sides of the cell.
U ssing et al ( 19 5 1) dem onstrated a potential difference across frogs' skin arising as a conse quence o f active transport. H e defined this as ion transport against an electro-chemical giad ient. Perhaps m ore w ell known arc the experim ents o f H odglin et al (1952) where the electrical activity o f nerves was shown to arise from the passage o f N a and K ions across the cell m em brane. N o t unnatur ally, workers turned to the kidney to study these processes as it is an organ where it is relatively easy to m ake electrical recordings and to determ ine ionic concentrations w ithout sub stantially altering the physiological conditions. Solom on (19 5 7), utilising the specialised electrodes developed in nerve and m uscle studies by L in g and G erard, observed a bim odal distribution o f potentials on random insertions into the tubules o f rats. D urin g the puncture, transient higher potentials were recorded indicating that the electrodes were passing through cells with a greater negativity than the lum en. T h e low er range was related to the proxim al and the higher to the distal tubules.
G iebisch in a m uch fuller investigation using the proxim al tubules o f N ecturus found a m ean value o f -72m V for the peritubular m em brane potential (i.e. the P .D . between the peritubular fluid and the inside of the cell) and of -20m V for the transtubular potential. B y difference, the lu m in a l mem brane p o te n tia l was about 52m V negative inside the cell. Reductions in these potentials were produced by oxygen lack and by m ercurial diuretics w hich have b o th been shown to reduce active transport pro cesses. (Fig. 2.) In investigations o f the transtubular poten tia l, d irect microanalysis showed no concentra tio n gradient between the p e ritu b u la r and tu b u la r fluids fo r Na, H and C l ions. T h e po te n tia l difference is not, therefore, m a in tained by io n ic concentration gradients. There m ust be one or m ore active mechanisms in volved. M a n y workers believe th a t Na is the o n ly ion actively transported w h ile the other ions fo llo w passively dow n the electro-chem ical gradients set up. I n N e c tu ru s , at least, there is probably some active K transport.
T h e p rim ary process can be regarded as a s h ift o f positive ions from the lum en leaving i t at a negative pote ntia l. T h is is a process requiring energy.
M icroanalysis also shows th a t the Na con centration inside the cell is less than th a t in the tu b u la r fluid . As shown above, the inside o f the cell is at a m ore negative p o te n tia l than the lum en so Na ions can passively enter the cell along an electrical and a chem ical concentia tio n gradient. H owever the opposite is true o f the pe ritu b u la r border so i t is logical to assume th a t the active mechanism is situated here. T h is appears to be substantiated by electronm icroscopy where the m ito ch o n d ria are shown to be alm ost exclusively situated on this border. T here is some evidence to suggest th a t K uptake in to the cell is lin ke d to this " sodium p u m p " as the concentration o f K in side is greater than w ould be expected if only passive forces were involved. (Fig. 3.) Plasma D ista l T u b u la r T u b u la r cells F u ild port in tubular Cells.

(a) linked with Na Pump (a) ? K pump (b) passive (b) passive
T h is in te rp re ta tio n is obviously oversim pli fied. Refined techniques in vo lvin g single nephron perfusion, measurement o f io n ic fluxes u tilis in g radioactive isotopes have all been used, b u t the calculations involved in these methods are com plex, and cannot be ade quately discussed here. I t w ould also be unwise to a tte m p t clear interpretations and explanations at this stage o f research.
M edicine is no longer an em pirical art. Soon i t w ill be inadequate to know sim p ly w hat alterations in blood and urine biochem istry indicate. T h e basic changes occurring at cellular and sub-cellular levels m ust be under stood. T h is article illustrates the lim ite d advances made in o n e small field b u t perhaps indicates also the trend o f research in the future.  Since the depots constitute by far the greatest part o f the body fats, it was assum ed that the turnover rate observed was that characteristic of the depot fat. T h e acceptance o f these results necessitated the im m ediate rejection of the long cherished idea that adipose tissue represents an inert lipid store, capable of change only during periods o f fasting or of excess in gestion of food.

R E F E R E N C E S
T h is " about face" in belief naturally stim u lated m any workers and confirm atory results appeared rapidly in the literature. T h u s, Shapiro and W erth eim er evaluated the oxygen uptake of adipose tissue in vitro and took the elem entary precaution, or so it appears now, of expressing their results in terms o f the fat-free w eight o f the tissue in this w ay dem onstrating that " depot fa t" (so-called) ranked am ongst the m ost active tissues in the body when judged by this criterion. In 19 4 2, T u erkischer and W ertheim er reported that all dietary regimens which enhance fat form ation also give rise to the deposition o f glycogen w ithin the adipose tissue cells. Furtherm ore, these authors pointed out that this accum ulation o f polysaccharide is associated with high respiratory quotients, often exceeding unity, indicating that active fat syn thesis is occurring. M ore recently, isotopic evidence o f fat synthesis in adipose tissue in vivo has been obtained by Fararger and G e rlach who found that the fatty acids o f rat m esenteric lipid have higher specific activities than those o f either liver or blood shortly after the injec tion o f radioactive acetate or glucose.
Isolated enzym es of adipose tissue have, to date, been studied relatively little bu t it m ay be assumed, from the fact that the tissue is cap able of perform ing such reaction sequences as those involved in respiration and fat and glyco gen syntheses that m any enzym e systems do occur in this tissue. T h e re is nothing to be gained by further discussion o f these systems here-suffice it to say that the m ain point estab lished by the endeavours to dem onstrate enzym ic activities in adipose tissue is its evident marked specialisation in terms o f lipid m etabol ism. W h ile m ost of those enzym es sought can be detected in this tissue, those concerned with fat m etabolism show an activity equal to or exceeding that of their counterparts in the m ost active tissues o f the body.
F o r m any years reports appeared sporadically in the literature of small am ounts o f 11011esterified fatty acid (N efa) which can be de tected in plasm a, but until the early 19 50 's this lipid fraction was w idely regarded as an artefact of isolation. A t this tim e, however, G ordon pointed out that certain observed " anom alies" in the electrophoretic m ob ility o f plasm a pro teins m ay be reproduced in vitro by the addi tion o f sodium oleate to plasm a prior to the application o f the separatory procedure. T h is provided the first d ue leading to the suggestion th a t N e fa m ig h t be a physiological com ponent o f the circulating lipids, b u t i t was n o t u n til a year had elapsed th a t G ordon and C herkes ascribed to this fraction an im p o rta n t role in the transport o f fats fro m the depots to the tissues fo r oxidation. T h is contention is sup ported by several lines o f evidence. F irst, it h as been shown th a t N e fa injected in to various experim ental animals has a circulating half-life o f the order o f only tw o m inutes, indicating its rapid removal from the blood.
Second, estimates made o f the arterio-venous differences in plasma N e fa levels across various organs have indicated that, fo r example, the myocardium of the fasted anim al is capable o f rem oving 0.3 M E qu ivalen ts o f N e fa from each litre of the perfusing blood. In order to assess the physio logical significance o f this process, the authors perform ed concurrent measurements o f oxygen uptake and, 011 the basis o f the assumption that the average m olecular w eight o f the fa tty acid taken up is 275 (i.e. a m ixtu re o f fa tty acids q u a n tita tive ly distributed about the h yp o th e ti cal C17 com pound), they arrived at the con clusion th a t the q u a n tity o f N e fa taken up by the heart if sufficient to provide the b u lk o f its energy requirem ent under the conditions o f the experim ent.
T h e next problem requiring explanation was the mechanism by w hich the constancy o f the arterial N e fa level is m aintained, a problem to w hich we shall return later. A t this m om ent, all th a t need be said is th a t all the tissues studied, in clu d in g liver, appeared, on the basis o f a rterio-venous difference studies, to be active in the extraction o f N e fa from the circulating fluid. T h e quest, therefore, was fo r a source o f N e fa and the investigators turned to the adipose depots. T h e y were n o t disappointed fo r i t was found th a t samples of blood from the long saphenous vein, w hich may be regarded as draining the adipose tissue o f the low er lim b alm ost exclusively, showed large negative arte riovenous differences indicative o f N e fa release.
Thus the pattern has emerged in w hich N e fa represents an im p o rta n t, readily available source o f oxidizable material whose concentration in the blood is the resultant o f its rate o f removal by the tissues and the rate o f its lib e ra tio n from the fa t depots.
W e may now turn our a tte n tio n to a con sideration o f the concept o f " caloric homeo stasis" . As was noted earlier, the concentration o f N e fa in the plasma is m aintained at a re la tively constant level, between the lim its 0-5-1 m E q per litre , despite the high rate o f re moval by the tissues w hich is observed in the post absorptive state. T h is im plies the opera tion o f some fa irly sensitive co n tro l mechanism capable o f relating the rate o f lib e ra tio n o f N e fa to the somatic requirem ent. I f we return fo r a m om ent to the w ork of G ordon and Cherkes in w hich the rate o f uptake o f Nefa by the myocardium was estimated, we find th a t their results apply o n ly to the fasting state. In fact, G ordon proceeded in 19 57 to repeat the ex periments and obtained sequential blood samples fo r the measurement of arterio-venous N e fa differences before, and fo r some tim e after, the adm W e have seen, then, that adipose tissue ap pears to exert its influence on lip id metabolism by adjusting the availability o f N e fa in accord ance w ith somatic requirements fo r an oxidisable substrate. T h is being accepted the central issue qu ite clearly becomes th a t o f the elucida tio n o f the nature o f the mechanism by w hich the adjustm ent is effected under physiological conditions. I t w ould be logical to suppose that the process is subject to hum oral and to nervous control and indeed, evidence th a t such is the case has been obtained by many investigators.
T h e first piece o f evidence regarding the role of nervous a c tiv ity was provided in 1922 by G o ering who pointed o u t th a t excessive nerve stim u la tio n provokes fa t loss from the adipose tissue situated w ith in the d is trib u tio n o f the affected nerve, whereas paralysis or nerve section results in a marked deposition of fat in the depots, the magnitude of which may be partially or totally masked by the associated atrophy of the somatic musculature. Then, in 1947, Clement reported that unilateral denerva tion of various fat bodies in the rat caused a diminution in the rate of depletion of trigly ceride from the denervated side during fasting. Such observations suggest that the nervous system may exercise a tonic effect upon Nefa liberation from fat depots. This concept has found confirmation in the work of Havel and Gotofen (1960) who investigated the role of the sympathetic nervous system in the metabol ism of free fatty acids and observed that admin istration of hexamethonium, a ganglion block ing agent, causes a reduction in plasma Nefa levels in the fasting dog. From observations such as these, it has been concluded that the sympathetic nervous system exercises a tonic influence on the adipose tissue which may pro vide for a continuous release of Nefa at a level which can be modified by insulin and other Immoral agents. In addition to this, variation in the intensity of sympathetic activity itself might be reasonably expected to exert a direct effect on lipid mobilization.
Many humoral agents have been implicated in the regulation of fatty acid exchange in adipose tissue. W e may begin by considering epinephrine. Administration of this hormone to fasting humans has been found consistently to give rise to very rapid and striking increases in the plasma Nefa content which can be attributed to an increased rate of mobilization from the fat depots (as shown by arterio-venous difference studies) (Gordon and Cherkes, 1956). In 1957, Wadstrom observed that 90 minutes after the injection of 0.01 mg. of epinephrine into rabbits there is a decrease in the triglycende content of the fat depots asso ciated with corresponding increases in the levels of glycerol, mono and di-glycerides. This evidence pointed to the conclusion that epine phrine activates lipolysis or, what amounts to the same thing, inhibits resynthesis of trigly ceride in the adipose tissue. More recently, it has been shown by Gordon and Cherkes (1958) that the addition of epinephrine to surviving adipose tissue, in vitro, accelerates the rate at which this tissue releases Nefa into the sur rounding medium.
Shafir et al. have pointed out two interesting facts in relation to the effect of epinephrine on lipid metabolism. In the first place they observed that this hormone gives rise to parallel increases of Nefa and lipiprotein which latter plasma constituent is, in all probability, formed by the liver in response to the increased availability of fatty acids. The second, and perhaps the more intriguing, obser vation made by this group is that epinephrine exerts a more rapid effect upon lipid than on carbohydrate metabolism. Thus it is found that the hormone gives rise to a primary elevation of Nefa levels in plasma which gradu ally return to normal as the blood glucose rises. This observation is in agreement with the earlier results obtained by the same group in 1959 which indicated that the Nefa response to epinephrine can be prevented by simultaneous administration of glucose and insulin. The observation finds confirmation also in the work of Goldfen and H avel which showed that the Nefa response to norepinephrine, administra tion of which does not lead to marked hyperglycacmia, is sustained for a much longer time than that produced by epinephrine itself. The interesting fact emerging from these results is simply that, in time of stress, it is the lipid stores on which the body depends as a primary source of energy.
The second endocrine organ which exercises a profound effect upon lipid mobilization from storage sites is the anterior lobe of the p itu it ary. Some four hormones of pituitary origin have been shown to exert control over fatty acid metabolism; these arc somatotrophin (growth hormone), thyrotrophic hormone (TSH), the corticotrophins (A C TH ) and prolactin. I t should be emphasised that the effects of A C T II and TSH are of peculiar interest in this connection, since, on the basis of in vitro studies, it is known that their action is not dependent upon the presence of their " target organs" , though, in the whole animal, the presence of these organs w ill modify the lipid response observed.
The evidence so far to hand suggests that all four hormones influence lipid metabolism in essentially the same way: somatotrophin, however, by a sort of historical accident, has been studied most intensely and so the effects of this hormone w ill be considered at greater length than those of the other three.
In 1944, Stetton and Salcedo, injected anterior pituitary extract into mice, a procedure known to give rise to a condition of " fatty liver" : they discovered by means of prior deuterium labelling that the excess hepatic lipid had been transported to that organ from the adipose storage depots.
T h e problems involved in the isolation of pure and homogeneous preparations o f the various p itu ita ry principles made fu rth e r pro gress in this field d iffic u lt and even today, render interpretation a m a tte r open to doubt.
However, in 1953, Greenbaum and M cLean reported th a t treatm ent o f rats w ith " p u rifie d " som ato tro p h in caused a very rapid increase in hepatic triglyceride co n ten t. In view o f the fact th a t the horm one is know n to increase the rate o f fa tty acid oxidation in the liver, and bearing in m in d the results o f Stetton and Salcedo above, it seems apparent that the O n purely t eleological grounds, Reiss proceeded to argue that it is logical to expect prolactin to exercise a fa t m obilising effect, especially in view o f the fact th a t Shaw and Petersen (1938) have claimed, on the basis of A / V lip id differences across the lactating udder, that more than enough circulating lip id , in w hat form they do n o t say, is abstracted f rom the blood by this organ, to account fo r the entire lip id content o f the m ilk . T h is effect o f prolactin was also claimed on the basis o f H oussay's observation th a t s o m a to tro p in and the corticotrophins can, at least in part, replace prolactin in the maintenance o f lacta tion in the hypophysectom ised anim al. A warning m ust be given at this p o in t concerning the va lid ity o f such " round ab o u t" arguments however, and the w hole status o f the re lia b ility o f observations based upon w ork w ith so called " pure" anterior p itu ita ry principles m ust be examined c ritic a lly before acceptance.
W e may now pass on to a consideration of insulin. Both the concentration and turnover of N e fa in blood are strikin g ly influenced by this horm one. In the norm al fasting animal and in the diabetic anim al, the circulating N efa level is decidedly increased and indeed, in severe k e to tic diabetes the m olar ratio o f fa tty acid to scrum album in may exceed seven, w hich is the m axim um num ber o f fa tty acid m ole cules w hich can be tig h tly bound by one m ole cule o f serum alb u m in , the norm al value being rather less than one (Goodm an and G ordon, 1958).
In 1958 D ole observed th a t the adm inistra tion o f insulin causes a marked fa ll in the plasma N e fa level o f norm al individuals. As in the ease o f epinephrine considered above, the action o f insulin is o f particular interest in that this horm one has been shown (D ole 1958) to exercise an effect more rapidly on circu la t ing lip id than on blood glucose. Once again, this may be regarded as a reflection o f the im portance of lip id metabolism in the liv in g animal.
In ad d ition to the in vivo findings outlined earlier, C h erkes and G ordon, in 1958, measured the rate o f release o f N e fa by epididym al fat bodies obtained from fasting rats, when these adipose tissue fragments were incubated in a m edium containing bovine serum alb u m in as an acceptor o f N efa. I n the absence o f the horm one it was found that the tissue release 1.57 µ m o f fa tty acid per gram per h our w hile, w ith the a d d ition o f physiological concentra-tio n o f in su lin a net uptake o f N efa fro m the m edium was observed, a m o u n tin g to 1.03 um per gram per hour. In o th e r words the tissue w hich was releasing Nefa, on the a d d itio n o f in su lin, was persuaded to take up N efa from the environm ent.
O th e r horm ones have been reported to m o d ify the m etabolic a c tiv ity o f adipose tissue b u t th e ir effects rem ain, in general, poorly understood and in the interests o f bre vity they w ill n o t be discussed here.
W e have seen, then, some o f the ways in w hich the uptake and lib e ra tio n o f fa tty acids by adipose tissue may be c o n tro lle d in vivo, b u t tw o very fundam ental questions now present themselves. F irstly, w hat is th e nature o f the stim ulus w hich causes the co n tro l m echanism to come in to play and secondly, how is the ne u ro /h u m o ra l in fo rm a tio n translated in to terms o f biochem ical process? T o n e ith e r of these questions, p a rticu la rly the latter, can d e fin itive answers be given at this tim e b u t in w hat follow s, some a tte m p t w ill be made to cla rify the situation insofar as i t is possible, presently, to do so. I f we consider the norm al physiological situation o b ta in in g in an organism, then i t is clear th a t the effect o f som atotrophin on lip id m etabolism , in the norm al a d u lt, may be assumed to be m ore or less negligible, though it may be significant in the young anim al in w hich the provision o f adequate am ounts o f oxidisiable substrate to the grow ing tissue is mandatory. In any event, i t seems m ore lik e ly than n o t th a t any physiological effect a ttrib u t able to som atotrophin w ill be to n ic in nature and n o t subject to rapid or marked fluctuation. O n the o ther hand, a ll o f the oth e r com pon ents o f the co n tro l m echanism are capable o f dynam ic variation dependent on tissue require ments from m o m e n t to m om ent. T im s, the m ob ilisation o f N e fa in response to sym path etic nervous stim u la tio n and to the release o f epinephrine by the adrenal m edulla is a biochem ical reflection o f the sensitivity o f the nervous system to various types o f stress, and is m ediated by the a c tiv ity o f the higher nerve centres. In su lin , w hich strongly in h ib its lib e r ation o f N e fa from depot fa t and, as we have seen, may actually prom ote fa tty acid uptake by adipose tissue, is liberated fro m the pancreas in response to the stim ulus o f high blood sugar levels acting directly upon the pancreatic cells. As I have said before, this provides an example of the close correlation existing between carbo hydrate and lip id m etabolism and explains the observed dependence o f plasma N e fa levels on the n u tritio n a l state o f the anim al. T hus, a fasting anim al may be expected to have a lo w blood glucose level associated w ith a high level o f circu la tin g N e fa b u t if an alim entary h y perglycacmia is established, the resulting increase in the level o f circu la tin g in sulin may be held to explain the rapid fa ll in plasma N e fa w hich is observed in such a situation.
T h e mechanism by w hich this final co n tro l is actually m ediated is rather m ore obscure. T h ro u g h o u t this article, reference has been made to the lip o ly tic a c tiv ity o f adipose tissue. T h e im p lic a tio n has been th a t the various com ponents o f the n euro-h u m oral con tro l system m o d ify the a c tiv ity o f tissue lipases. C learly, however, an exactly parallel situation w ould arise if co n tro l was exercised by m o d ifi cations in the rate o f synthesis o f triglyceride w ith in the adipose tissue cells.
L e t us examine these possibilities. F irst, the lipase hypothesis. K orn and Q uigley found in 1957 th a t the o nly lipase a c tiv ity demonstrable in m any types o f adipose tissue was that due to heparin activated " lip o p ro te in lipase" . W h a t then o f N e fa release: in this case the substrate is rather d iffe re n t-n o t lip o p ro te in as in plasma, b u t m ore or less pure neutral fat (triglyceride) a fact th a t appears to rule lip o p ro tein lipase a c tiv ity o u t o f co u rt since the a c tiv ity o f the enzyme toward pure triglyceride is vanishingly small. W e m ust turn, then, to consideration o f the second hypothesis, that dealing w ith rates o f reeste r fication.
In 1 960, W o o d et al. pointed o u t th a t in rat epididym al fa t tissue, glucose carbon is incorporated in to the glycerol m oeity o f triglyceride at a rate m any times greater than the carbon of glycerol itself: they went on to demonstrate that adipose tissue homogenates require. L-a-glycero-phosphate or one of its phosphorylated precursors for optimum esterification of carbon labelled palmitate, glycerol itself being inactive in this system. If this is equally true of intact adipose tissue, then esterification of Nefa should be limited by the rate of formation of L-a-glycero-phosphate from glucose via di-hydroxy-acetone-phosphate.
Now it is known that the triglyceride of adipose tissue undergoes constant hydrolysis ancl re -esterification within the tissue; by what mechanism the hydrolysis is effected is not understood. However, it must be assumed on this evidence that, in the steady state condition, where there is no net uptake on release of Nefa, the liberated fatty acids are rapidly re-esterified. This re-esterification re quires the presence of a supply of l-a-glycerophosphate obtained by the metabolism of glucose via the Em bden-M eyerhof pathway. The equilibrium situation between triglyceride and Nefa within the cells is quite obviously dependant upon a ready supply of glucose. During periods of hypoglycaemia, the Nefa of the adipose tissue might be expected to rise and since intracellular and extracellular Nefa arc in a free translocation relationship this will lead to their liberation into the blood; con versely, after glucose and insulin administration the enhanced respiratory activity of the adipose tissue cells w ill ensure a plentiful supply of dihydroxy acetone phosphate and therefore of L-a-glycero-phosphate so that the fatty acid level of the circulating fluid will diminish as Nefa is withdrawn to be esterified within the cells.
This hypothesis has been found to accord well with experimental data in which the per centage of glucose carbon incorporated into the glycerol moiety of neutral fat has been estimated under varying conditions of availa bility of glucose. It provides an elegant ex ample of the indirect way in which hormonal substances may modify cell metabolism since the action of insulin on fatty acid mobilization appears in this way to be explicable in terms of a primary action of the hormone, notably that of influencing the translocation of glucose across cell membranes. Attractive though the hypothesis may be, however, a note of caution must be sounded-the energy transformations and relationships in systems such as this remain obscure, complicated as they are by the very peculiar solubility properties of the participat ing lipids and lipoproteins and estimations of equilibrium constants for such systems have not, so far, been attempted.
In this article a very few of the ad vances which have been made towards the understanding of adipose tissue and its role in lipid metabolism have been discussed. W e have considered the recognition, some thirty years ago, of the fat depots as dynamic entities, the discovery of the significance of Nefa in metabolism and the possible means by which the control of lipid uptake and release by adipose tissue may be affected under physiolo gical conditions. W h at has emerged is still a far from coher ent story and we can only wait, perhaps for a further quarter of a century in the hope that the final word may yet be spoken.