1218 PHYSIOLOGY 



chemical substances produced in the ovaries. According to some authors, 

 the essential factors for the production of these genital hormones are the 

 ' interstitial cells ' found both in the testes and ovaries of various animals. 

 These interstitial cells are not, however, universally present. It has been 

 shown that, by means of the Rontgen rays, it is possible to destroy the 

 germ-cells in either testes or ovaries, so rendering the animal sterile. The 

 interstitial cells, when present, are not destroyed by these rays, yet the 

 effects on the accessory genital organs are stated to be as marked as after 

 complete extirpation of either ovaries or testes. 



The chemical correlations between the ovaries and the other organs 

 concerned in reproduction are perhaps best marked in the changes which 

 attend pregnancy. In this case the fertilisation of the ovum by a sperma- 

 tozoon is followed by a great development, first of the mucous membrane 

 and later on of the muscular wall of the uterus. The mucous membrane 

 thickens, apparently in order to form a bed for the developing fertilised 

 ovum. With this growth of the uterus there is a corresponding growth of 

 the other parts of the genital tract, e.g. the vagina. At the same time rapid 

 changes take place in the mammary glands. These changes may be studied 

 experimentally in the rabbit, in which animal gestation lasts only about 

 twenty-nine days. In a virgin rabbit of a year old it is difficult with the 

 naked eye to see any trace of the mammary gland in the tissue lying under 

 the nipples. Each gland is limited to an area not more than 1 cm. broad, 

 and consists entirely of ducts lined with a single layer of flattened epithelial 

 cells. With the occurrence of conception a marked change takes place. 

 Four or five days after fertilisation, when it is still impossible with the 

 naked eye to discover any embryos in the swollen uterine horns, on reflecting 

 the skin from the abdomen each mammary gland appears as a circular pink 

 area, about 3 c.m. in diameter. On section the gland consists of ducts 

 which are in an active state of proliferation, their epithelial lining being 

 two or three cells thick and presenting numerous mitotic figures. 'By the 

 ninth day the whole abdomen is covered with a thin layer of glandular 

 tissue ; by the twenty- fifth day this tissue is J cm. in thickness and consists 

 for the greater part of secreting alveoli, lined with cells containing numerous 

 fat-globules. At full term the alveoli contain ready-formed milk. 



This, hypertrophy of the mammary glands occurs during pregnancy 

 after complete division of all possible nervous paths between the glands of 

 the ovaries or uterus. In the guinea-pig a mammary gland has been actually 

 transplanted to another part of the body, thus severing all its normal nervous 

 connections, and yet it enlarged as usual during a subsequent pregnancy. 

 Ancel and Bouin have brought forward evidence that the corpus luteum 

 the tissue produced in the ovary as a result of the discharge of an ovum- 

 is intimately concerned with the growth of the mammary glands, and may 

 indeed cause a certain degree of hypertrophy of these glands in the entire 

 absence of any product of conception within the uterus.* The limited 



* According to Ancel and Bouin, in the rabbit discharge of an ovum and formation 

 of a corpus luteum only occur as a result of copulation. The same effect may be pro- 



