438 



ORGAN SYSTEMS OF MAN 



Fig. 16-30. The removal of the single ovary in birds results in the subsequent development of testes and male 

 characteristics. In these photos the chickens on the extreme ends are female and male respectively. The animal 

 in the middle had its ovary removed at seven w^eeks of age and shows a vt^ell-developed male comb. Autopsy 

 showed two fully formed testes. 



particularly talented youth, castration did 

 the trick, and thus choirs could be pro- 

 duced with remarkable musical qualities. 

 Occasionally, the accidental loss of the 

 testes in a young boy has resulted in an 

 adult with a high-pitched voice, lacking a 

 beard, obese and with little of the ambition 

 and the usual emotional characteristics 

 associated with the male. Castration after 

 maturity, however, seems to initiate few, if 

 any, of these changes. 



The onset of interstitial tissue activity is 

 associated with puberty when pubic hair, 

 change of voice, and increased size of the 

 genitalia occur. 



If testosterone is injected into a castrated 

 animal or a testis is transplanted into some 

 part of the body where it can grow and 

 secrete testosterone into the blood stream, 

 the male secondary sexual characters will be 

 restored. Such injections given to a cas- 

 trated female will cause it to develop 

 masculine characteristics. A perfectly nor- 

 mal egg-laying hen can be induced to be- 

 come a functional father rooster with comb, 

 wattles, and crow and all by castration fol- 

 lowed by a series of injections of testos- 

 terone. By removing the single ovary from 

 a seven-weeks old chick a normal "rooster" 

 will result (Fig. 16-30). This can be ac- 

 complished in female birds because they 

 possess a residual testis and no external 

 genitalia. Sex reversal in mammals is 

 limited to the secondary characteristics 

 only. 



Occasionally the testes in mammals fail 

 to descend normally into the scrotal sac as 

 they should do during the last few weeks of 

 gestation. This condition is known as crypt- 

 orchidism and males in which it occurs are 

 invariably sterile. If, however, the testes 

 are brought down into the scrotum by 

 surgery, they very soon become functional 

 and produce viable sperm. A cryptorchid is 

 perfectly virile in every way except fertility, 

 that is, he possesses all of the normal char- 

 acteristics of the male including sex drive. 

 This is because his interstitial tissue is un- 

 impaired, so that testosterone is produced 

 in proper amounts to allow for normal 

 development of his masculine character- 

 istics. Upon microscopic examination, these 

 testes will show perfectly normal interstitial 

 tissue but degenerate non-functional sperm- 

 producing tubules. Experiments show that 

 if the normal testes of mammals are placed 

 back into the body cavity or heated to the 

 internal temperature of the animal the 

 sperm tubules degenerate. Therefore, ster- 

 ility of the cryptorchid is due to the higher 

 temperature existing in the body as com- 

 pared to the scrotal sac. This is difficult to 

 correlate with the fact that the internal 

 testes of birds are fertile and the tempera- 

 ture is even higher than that of mammals. 

 In the long evolution of mammals one fails 

 to note the advantage of placing these or- 

 gans, upon which the race depends for its 

 perpetuation, in such a hazardous position 

 when they would be much safer housed 



