HORMONES AND REPRODUCTION 63 



this type of molecule alone, and other oestrogenic 

 substances which are apparently chemically unrelated 

 have been manufactured in the laboratory and used in 

 medical practice. 



The method of standardisation of such oestrogens 

 gives an indication of their normal function. Solutions to 

 be tested are usually injected into mice from Which the 

 ovaries have been removed, and the effect is looked for 

 in the cellular content of the vagina. The typical action 

 of these substances is to cause the growth of the 

 Miillerian duct system. 



Indeed, a fundamental effect of oestradiol on the body, 

 like that of testosterone, may be the stimulation of cell 

 division, whence these substances have also been called 

 mitogenic hormones.^'^ However, those organs which 

 are especially sensitive to oestrogenic stimulation are the 

 oviducts of the egg-laying vertebrates and the vagina, 

 uterus, and mammary glands of the mammals. Con- 

 sequently, it is these organs which have been mostly 

 studied, and only recently has it been realized that 

 a variety of other tissues, such as the epidermis and the 

 lining of the oesophagus, may react in much the same 

 way. The degree of reaction of various tissues to the 

 presence of oestrogens may vary widely, but as in the 

 male it is evident that most, if not all, body organs have 

 the potentiality of enlargement in relation to sexual pro- 

 cesses should special need arise. It must have been 

 in such a manner that the mammary gland was evolved 

 in those vertebrates which suckle their young. 



It has also teen realized only recently that oestrogens 

 have important functions to fulfil inside the ovary 

 itself. 6' ^5' 93 As usual, conditions are best understood 

 in the mammal, and they may be summarised as follows. 

 When the follicle-stimulating-hormone of the anterior 

 pituitary induces rapid growth of a Graafian follicle, 

 part of this growth is achieved by mitosis and part by the 

 secretion into the antrum of the follicular fluid. ^3' ^^ Jt 

 is well known that this fluid has a high oestrogen content, 



