CHEMICAL CORRELATION OF ORGANS OF GENERATION 379 



of the embryo and the development of the Mammary Glands of the 

 mother. .As the fetus grows the mammary glands of the pregnant 

 female hypertrophy until a portion of the hypertrophic tissue begins to 

 break down^and give rise to a secretion of milk, and this stage of 

 development is attained at the moment when the fetus is approaching 

 the full term of gestation, and is about to be delivered. 



It has been ascertained that this remarkably exact synchrony of the 

 development of such widely separated organized bodies as the fetus 

 and the mammary glands of the mother is brought about by the circu- 

 lation in the blood of some as yet unindentified substance which is 

 elaborated by the tissues of the Placenta. If a saline extract of the 

 placentae of rabbits be injected repeatedly into the circulation of virgin 

 rabbits, the mammary glands hypertrophy just as they would if the 

 animal were pregnant, and finally secrete milk which may be expressed 

 from the nipples. Another factor, however, which may possibly 

 contribute to the development of the mammary glands and their secre- 

 tion of milk is the slight measure of hypertrophy of the Pituitary Gland 

 which invariably accompanies pregnancy. The boiled aqueous extract 

 of the posterior lobe of the pituitary gland contains a nitrogenous base 

 of unknown constitution, designated Pituitrin, which increases the 

 irritability of the muscular walls of the uterus, causes an increase in the 

 volume of the urine and stimulates the secretion of milk, the latter 

 effect being a very unusual one for any pharmacological agent to bring 

 about. The large and repeated dosages of placental extract which 

 Starling and Lane-Claypon found to be necessary to bring about the 

 degree of hypertrophy of the mammary glands which is requisite for the 

 production of milk may possibly have been attributable to the absence 

 of the assistance, in these experiments, which is afforded in actual 

 pregnancy by the enhanced activities of the pituitary body. 



That the hyperdevelopment of the mammary glands of the mother 

 is due to the presence of stimulators circulating in the blood, and not 

 to any reflex nervous stimulation of the glandular tissues, is shown, not 

 only by the above-cited experiments, but also by the fact that the effect 

 of these substances is not confined to the mother, but extends to the 

 embryo, which is not connected by any nervous channels with the 

 tissues of the mother. It is a familiar fact that the breasts of newborn 

 infants frequently secrete a few drops of milk or may be made to do so 

 by brief manipulations of the nipples. The milk thus obtained was 

 known in former days as "witches' milk" and was accredited by the 

 lady practioners of a hundred years ago with many important proper- 

 ties of a supernatural description. 



When the development of the embryo has reached a certain stage, 

 Uterine Contractions bring about the expulsion of the fetus. We have 

 here another example of curiously exact coincidence in time. It is not 

 a question of the size of the developing fetus ultimately bringing about 

 such a degree of distention of the uterus as to induce a special tendency 

 to contraction, for even the same individual may deliver infants in 



