The thymic hormones.

The existence of a specific hormone of the thymus could be demonstrated with the traditional tests: The observation of the consequences of thymectomy. The possibility to suppress these consequences by a specific therapy. This succeeded by means of thymic grafts and by means of injections of an adequate thymus extract. (Several extracts of demonstrated substitutive potency have been prepared.) A presumably pure chemical entity was isolated, which suppresses the consequences of thymectomy as completely as the total extract. There is circumstantial evidence for the assumption, that under normal conditions this substance is secreted into the circulation. Lymphocytes act presumably as its vectors. The most conspicuous features of the physiological role of the thymic are: (1) Its influence upon the lymphocytes. (2) Its interactions with other hormones. (3) Its role in the development of the immunitary reactions. The complete study of the functions of the thymus under all these aspects has been performed thus far only with the presumably pure substance mentioned above. The question, whether the thymus secretes one or several hormones, can not be answered thus far. (A mention is made of the substances obtained from the thymus and active on the growth of malignant tumours.)