148 READINGS IN BIOLOGICAL SCIENCE 



the adrenals are stimulated to an increased output of adrenalin. This, in 

 turn, supplies the body with muscular power to resist or carry out any 

 of the actions that may take place under these emotions for the welfare 

 or preservation of the individual. The sugar of the blood — the most favor- 

 able source of muscular energy — increases in quantity; if digestion is in 

 progress its activities are suspended and the blood is shifted to the organs 

 immediately necessary for muscular exertion — the lungs, heart and central 

 nervous system; the blood becomes more coagulable; heart action be- 

 comes more vigorous; muscular fatigue is counteracted by the extra hor- 

 mone; in brief, such fundamental readjustments are instituted as are favor- 

 able to great feats of strength or endurance, whether these be fighting 

 or running away. 



The hormone activities of the gonads have long been known. Ovaries 

 and testes alike, besides forming germ cells, also produce internal secre- 

 tions which influence the individual profoundly, both physically and 

 mentally. The male gonads or testes have so-called "interstitial tissue" dis- 

 tributed throughout, between the sperm-producing tubules, and it is 

 from such interstitial glandular cells that the male sex hormone, testosterone, 

 is supposedly derived. Castration of male domestic animals is a common 

 practice and the modifications of the distinctively masculine features 

 that result are strikingly apparent. Also, larger, fatter and more docile 

 animals are thereby secured. Even human beings have frequently been so 

 treated, and it is only within relatively recent times that the castration of 

 boys to provide high-pitched voices for cathedral choirs has been aban- 

 doned. Once the secondary sex characters have appeared, however, they 

 are unaffected by later castration. 



Much experimentation has been in progress with the lower animals in 

 recent years and many significant facts regarding the sex hormones have 

 been discovered. It has been found, for example, that the suppression of 

 the secondary sex characters and accessory reproductive structures can 

 be prevented in the young developing male castrate if repeated injections 

 of testicular extracts or the male sex hormone, testosterone, are given. 

 Testosterone has not only been isolated in pure form but can be artificially 

 synthesized by the biochemist. In such mammals as the rat or guinea pig, 

 if the ovaries of a female are transplanted into a male which has been 

 previously unsexed, the latter under stimulus of the ovarian secretions 

 assumes a behavior like that of the female. Its hair and skeleton come to 

 resemble more those of the female than of the male, and its rudimentary 

 milk glands become enlarged to functional size. If the ovary of a Mallard 

 duck is completely removed, at the succeeding moult she takes on the 

 very different plumage of the male. Likewise, if the ovaries are removed 

 from very young hens they develop to a greater or lesser degree the more 

 ornate plumage, the spurs, wattles, comb and larger size of the cock. The 

 development of these characteristics will be still further increased if extract 



