THE HORMONES IN PREGNANCY 



Fig. 29. Diagrams illustrating the development of the mammary gland 

 as seen in laboratory animals. A, mammary gland of immature animal, 

 consisting of simple ducts radiating from the nipple. B, small area of A 

 enlarged to show adult virginal gland. The action of estrogenic hormone 

 has produced extensive growth and branching of the ducts. C, small part 

 of B enlarged again to show the effect of pregnancy; there has been a 

 great development of duct twigs with terminal alveoli. D, terminal alveoli 

 enlarged to show their cell-structure. E, secretion of milk globules by the 

 cells of the alveoli. Based on a figure by C. W. Turner In Sex and 

 Internal Secretions. 



perhaps in the ordinary cycle, in which the corpus luteum 

 lasts but two weeks, there is not time to build up the mammary 

 gland sufficiently. He therefore ingeniously proposed to apply 

 the discovery, then quite new, that the corpora lutea can be 

 made to persist for weeks by injection of anterior pituitary 

 extract. He tried this experiment in rabbits, by mating them 

 to males rendered infertile by having their seminal ducts 



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