THE HORMONES IN HUMAN REPRODUCTION 



like that found in extracts of beef pituitary glands is respon- 

 sible for the secretion of the protective jelly of the eggs of 

 toads. She elicited this function by inserting pieces of toad 

 or beef pituitary gland under the skin of her toads, thus in- 

 creasing the available amount of pituitary hormones; and 

 in a few cases she could even elicit it by injecting Riddle's 

 prolactin. 



Here, then, are three particular means of provision for the 

 newborn infant, occurring in three widely different branches 

 of the animal kingdom, and adapted to offspring living under 

 very dissimilar circumstances, yet all these secretions are con- 

 trolled by the pituitary gland and can be induced by extracts 

 of beef pituitaries. The embryologist perceives a further 

 remarkable feature of this story. The mammary gland, he 

 knows, is derived from the outer of the three fundamental 

 tissue layers of the embryo, the ectoderm'^ the crop glands 

 of the pigeon are derived from the inner layer, the endoderm ; 

 and the secretory lining of the toad's oviduct is derived from 

 the middle layer, the mesoderm. These three tissues from which 

 the pituitary gland elicits reactions of such similar useful- 

 ness, are about as widely different in their position in the 

 body, and in their embryological history, as they can possibly 

 be, but when in the evolution of toad, bird, and mammal there 

 was need to call upon them to foster the fledglings of their 

 kind, the pituitary gland took control in each case. 



Has the corpus luteum, then, no role whatever in the proc- 

 esses leading to lactation, and can the pituitary extracts in- 

 duce lactation in a mammary gland prepared only by estro- 

 genic hormone.'* My rabbits seemed to indicate that this is 

 true, but Strieker and Grueter declared that their pituitary 

 extracts were not successful unless there had been corpora 

 lutea in the ovaries at some time during recent months ; in 

 other words, the pituitary lactogenic hormone appeared able 

 only to jact upon a mammary gland sensitized by progeste- 

 rone. This difference in the findings led to a great deal of 



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