As the thyroid gland, as any other endocrine organs, is responsible for the mental as well as the bodily development, it has, been advocated by E. Kretschmer, G. Eward, W. Jaensch, M. R. Berman, O. Klieneberger and other psychologists and characteologists that the thyroidhas a great effect upon the human character. Above all, Berman insisted in his The Glands Regulating Personality upon that the thyroid internal secretion has a very definite controlling relation to intelligence and the complexity of the convolutions of the brain, and that when the chemical reactions which depend upon the thyroid go faster, more oxygen and food materials are burned up or oxidized, more energy is liberated, the metabolic wheel rotates More quickly, the individual senses, feels, thinks and acts more quickly. But his theory is imaginative and speculative, lacks the exact psychological experimental ground.
We began this study for the purpose of detecting the effect of the thyroid gland upon the behavi6ur and learningabilityof animals. For this purpose, we used 32 albino rats and 12 mice and we sorted them into pairs of the same breeding according to their age, sex and weight?\one group for experimental and the other for control animals. To ah experilnental albino rat, we administered the desiccated thyroid gland every day successively 0.005 gm. per 100gm. of its bodily weight and to an experimental mouse 0.0006gm. for some days. Then after about ten days, we experimented on the albino rats by the Obstruction Method, the Maze Learning Method, the Choice Box Method and on the mice by the Revolving Wheel Method. The results of the observations and experiments are as follows:
1) The behaviour of the hyperthyroid rats was more stimulating, more smart ahd more active than that of control rats.
2) The former crossed over the water funk in the obstruction box sooner than the latter. See Fig. 6 in the Japanese Text, pp.344 & 345)
3) In the maze learning, the former eliminated the blinds more readily and reached to the goal sooner than the latter. (See Fig. 8 and Fig 9 in the Japanese Text, pp. 350-1 and 353)
4) The hyperthyroid mice revolved the wheel in the revolving wheel cage more than 10,000 times in six hours in the first trial day in spite of the fact that the control revolved only a few hundred times. But the former hardly improved in revolving the wheel by learning, while the latter revolved more and more times till they surpassed the former in revolving times by above 2,000 times after one week's learning. (See Fig. 12 in the Japanese Text p.359)
5) The above mentioned changes in the behaviour and learning ability of the hyperthyroid animals seemed to appear from five to ten days after the beginning of administrating the desiccated thyroid gland.
6) When we discontinued to administer the desiccated thyroid gland, the animal became less active and less stimulating. We could not make clear whether the improved learning ability would change afterwards again or not.
7) We could not know how these changes happened. In order to find out: whether these changes came from the hunger of the hyperthyroid animals, we tried an experiment, but could not get to any conclusion.