THE HORMONE OF PREPARATION 



of its response by such changes in the vaginal wall and in 

 the free vaginal cells as we have already discussed and 

 illustrated (page 83; Plate XV). In human females who 

 have passed the menopause, and younger women whose 

 ovaries have been removed surgically, the vagina shows the 

 effect of diminished or absent estrogenic hormone. When 

 such patients are given the hormone, its effect can be detected 

 by studying the vaginal cells. This method is now used to 

 diagnose loss of ovarian function and to follow the progress 

 of treatment with hormones. 



The estrogenic hormones act on the mammary glands in 

 a very definite way. These glands, when fully developed, 

 are constructed on a plan resembling a little cluster of trees, 

 in which the trunks come together at the nipple, forming 

 the main milk canals. The branches form the general duct 

 system, and the leaves are the milk-producing units (see 

 Fig. 29). In immature animals the twig-like terminal units 

 are scarcely or not at all developed, and even the duct sys- 

 tem is rudimentary. Estrogenic hormones make the ducts 

 grow until the gland is a wide-spreading tree, but still with- 

 out much development of the actual milk-producing termina- 

 tions on the ends of the twigs. In short, the estrogens bring 

 the infantile mammary glands up to the normal stage of 

 development of a mature virgin animal. As we shall see in 

 Chapter VIII, during pregnancy other hormones, namely 

 the pituitary hormones and in some animals the corpus 

 luteum hormone, carry on the development of the gland and 

 bring about the production of milk. 



The estrogens and puberty. When the time approaches for 

 a young girl to become mature, the pituitary gland begins 

 to put out its gonadotrophic hormones (see p. 141). These 

 in turn stimulate the ovary to produce its estrogenic hor- 

 mone. All the accessory reproductive organs (uterus, ovi- 

 ducts, vagina, external genital organs, mammary glands) 

 begin to grow toward mature size. The menstrual cycle 



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