THE HORMONES IN HUMAN REPRODUCTION 



led by Philip E. Smith, now of Columbia University, has been 

 the discovery (1927) that removal of the pituitary gland 

 from an adult male causes degeneration of the testis, and 

 in an immature male prevents the development of sperm cell 

 formation. The implantation of bits of pituitary gland or 

 the injection of pituitary extracts will substitute for the 

 missing organ and prevent degeneration of the testis. In some 

 species, but not in others, success has been attained in start- 

 ing sperm formation in immature animals by injecting pitui- 

 tary extracts. 



Another remarkable discovery about spermatogenesis was 

 announced by Carl R. Moore (University of Chicago) in 

 1924, namely, that the mammalian testis cannot form sperm 

 cells unless it is subjected to a temperature slightly lower 

 than that of the interior of the body.^ In its normal place 

 in the scrotal sac the testis is under temperature conditions 

 exactly suited to its function. It has long been known that 

 a man with undescended testicles is not fertile, and horse 

 breeders are well aware that the same is true of cryptorchid 

 stallions. They often call upon veterinary surgeons to bring 

 down the testes of colts by operation. Moore's investigations 

 have given us the reason for this sterility. In man descent 

 of the testes normally occurs before birth. The sex glands 

 are formed in the abdominal cavity near the lower pole of 

 the kidneys, but they gradually move downward (or as some 

 embryologists prefer to say, the body grows upward past the 

 testes) until they have fully descended and have occupied 

 their permanent place in the scrotum. Just why this elaborate 

 transfer of the testes takes place, seemingly leaving them 

 less protected than if they remained in the abdominal cavity, 

 as in lower vertebrate animals, has never been satisfactorily 

 explained. One can only guess that when the process of evolu- 



1 For a full account of this subject, see Sex and Internal Secretions, 

 edited by Edgar Allen, 2d ed., Baltimore, 1939; Chapter VII, "Biology 

 of the Testes," by Carl R. Moore. 



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