The morphological changes of single cells on a cover slide previously inserted into subcutaneous tissue of rabbits or guinea pigs pretreated with tubercle bacilli or other antigens were observed under a supravital condition by adding antigens from tubercle bacilli or corresponding antigens. Old tuberculin or tuberculo-protein provoked "cellular shocking" on cells from tuberculo-sensitized animals, but not from non-sensitized. The "shocking" represented cellular constriction forming cilliary projections at first and many blisters lately on the surface of the cells. The time course of the shocking was about 6 to 8 hours and this corresponded to the delayed type of allergic reaction. Protein antigens such as egg albumin or allogenic sera caused minimal morphological changes because of the acute death after anaphylactic reactions of the sensitized cells. Reactions on cells after immersing in their antisera from allogenic animals were intensive enough to occur prompt plasmolysis and cell explosion. These morphological changes on a single cell corresponded to the immediate type of allergic reaction.