The changes that the mammary glands undergo during pregnancy whereby they become adapted to the physiologic function of lactation when parturition takes place have been the occasion for much speculation and some experimental study. Secretory nerves to the glands have not been discovered, so that the evolution of the mammary structures to a form and condition that permit the production of milk is in all probability initiated through humoral rather than nervous paths. This view is further substantiated by the discovery that the mammary glands may develop and function under conditions that preclude the possibility of a nervous connection with other parts of the organism; for example, when mammary tissue was transplanted to an abnormal position in the body.
A quarter of a century ago Starling and Lane-Claypon of London pointed out that, since the mammary gland normally undergoes enlargement and histologic change preparatory to the secretion of milk during
THE HORMONAL CONTROL OF LACTATION. JAMA. 1931;96(5):359-360. doi:10.1001/jama.1931.02720310049013