The Testicular Hormone.*

The preparation of testicular extracts has for the last 3 years been subjected to intensive investigation by this laboratory. McGee (1) and McGee, Juhn, and Domm (a), have shown that extracts of the lipid fraction of bull testicles exert a striking effect on the secondary sex characters of the Brown Leghorn capon. Gallagher (3) has shown that by the present methods of extraction and assay this activity is found in no other tissue save testis and epididymis. Moore and McGee (4) have shown these extracts to possess the same activity as the internal secretion of the testis by their effect on the spermatozoa in isolated epididymides according to the criterion proposed by Moore (5). These results in the mammal have been extended by Moore and Gallagher (6) with more highly purified preparations and some attempt has been made to investigate this reaction as a means of quantitative assay. A further new series of indicators has been proposed by Moore and Gallagher (6, 7), Moore, Price, and Gallagher (8), and Moore, Hughes, and Gallagher (9)) based upon cytological changes in the accessory reproductive organs and the secretion of the seminal vesicles and prostate gland. These varied biological manifestations of the testis hormone have been developed by the Chicago group in hope of attaining some rapid quantitative method of assay for testicular extracts. An extensive investigation of the comb growth reaction in the