During our recent investigation1 of the influence of endocrine substances on the development of the mammary gland of the rat, a number of mammary abnormalities were experimentally induced. The possibility that some of these observations may have a bearing on diseases of the human breast made it desirable to study the changes further.
It is our purpose in this paper to present the more pertinent results and to suggest their possible relation to mammary disease in human beings.
A number of workers have observed abnormalities in the mammary glands of animals into which various endocrine substances were injected. Evans and Simpson2 noted extensive mammary development following injection, for long periods, of pituitary extracts into rats; excessive epithelial proliferation and formation of fibro-adenoma occurred in noncastrated females. No effect was obtained in castrates, since the changes are mediated through an effect on the ovaries. Howard3 recently obtained similar