THE FEMALE REPRODUCTIVE ORGANS. 985 



through the blood rather than through the nervous system. Some 

 direct evidence for this point of view is furnished by the interesting 

 experiments of Starling and Lane-Claypon.* These authors found 

 that extracts made from the body of the fetus, or rather from the 

 bodies of many fetuses, when injected repeatedly into a virgin rabbit 

 caused a genuine development of the mammary glands closely 

 simulating the growth that normally occurs during pregnancy. 

 Since similar extracts made from ovaries, placental and uterine 

 tissues had no effect, they conclude that a specific chemical sub- 

 stance (a hormone) is produced in the fetus itself and, after absorp- 

 tion into the maternal blood, acts upon the mammary gland, stim- 

 ulating it to growth. Since the birth of the fetus is followed by 

 active secretion in the mammary glands they adopt further the 

 view that this substance, while promoting the growth of the gland 

 tissue, inhibits the catabolic processes which lead to the formation 

 of the secretion. With the birth of the fetus this substance is 

 withdrawn and secretion begins, and, on the contrary, the secretion 

 is suspended when a new pregnancy is well advanced. Further 

 evidence of the same kind is furnished by the interesting case of the 

 Blazek sisters.f These twins had a common circulation but sepa- 

 rate nervous systems. Pregnancy and parturition in one was 

 followed by a secretion of the mammary glands of both. 



As was said in speaking of the histology of the gland, the se- 

 creting alveoli are not fully formed until the first pregnancy. Dur- 

 ing the period of gestation the epithelial cells multiply, the alveoli 

 are formed, and after parturition secretion begins. As the liquid 

 is formed it accumulates in the enlarged galactophorous ducts, and 

 after the tension has reached a certain point further secretion 

 is apparently inhibited. If the ducts are emptied, by the infant 

 or otherwise, a new secretion begins. The emptying of the ducts, 

 in fact, seems to constitute the normal physiological stimulus to 

 the gland-cells, but how this act affects the secreting cells, whether 

 reflexly or directly, is not known. 



The possibility that the mammary secretion is influenced by 

 various internal secretions has been brought out by the experiments 

 of Ott and Scott. J These observers find that extracts of several 

 glands, particularly of the posterior lobe of the hypophysis and of 

 the corpus luteum, have a distinct stimulating effect upon the 

 mammary gland. Whether or. not this influence is exerted nor- 

 mally remains to be determined. 



Composition of the Milk. The composition of milk is com- 



* Lane-Claypon and Starling, "Proceedings of the Royal Society," 1906, 

 B. Ixxvii.; see also Starling in "Lancet," 1905. 



t Basch, "Deut. Med. Wochenschrift," 36, 981, 1910. 



j Ott and Scott, "Therapeutic Gazette," Oct., 1911, May and Nov., 1912. 



