PHYSIOLOGY OF SEX AND REPRODUCTION. 231 



which furnishes the most tragic possibilities of the life of woman, 

 becomes thus less mysterious. We can understand more readily the 

 association of such diseases with much of what we are pleased to gen- 

 eralize as civilization, and view more hopefully the possibilities of their 

 enormous diminution by the rational hygiene of civilization properly 

 so-called. 



The milk or mammary organs are modified skin-glands, probably 

 most nearly allied to the ordinary sebaceous type, except in mono- 

 tremes which appear to be divergent. Every one knows that they are 

 exclusive characteristics of mammals, and are only normally functional 

 in the female sex. Rudimentary in the males, they may even there 

 produce milk ("witches' milk") at birth, puberty, and under patho- 

 logical conditions, while cases have been put on record of men who 

 have actually given suck.* They vary greatly in position and num- 

 ber, a large number being doubtless the primitive condition. In 

 function, after the birth of offspring, the surrounding tissue is specially 

 rich in white blood-corpuscles, which probably form some of the 

 structural elements of the milk. It has also been shown that the 

 nuclei of the gland-cells undergo degeneration, disruption, and expul- 

 sion, and that they in all likelihood form the casein elements of the 

 nutritive fluid. 



Before birth, the mammalian embryo has been nourished through 

 the placenta, by the transfusion already referred to. The alimentary 

 canal has obviously had no experience in digestive function. Before 

 it proceeds to digest the food of the parents, it is put through a course 

 of what Sollas neatly terms "gastric education," by feeding upon the 

 readily assimilated mother's milk. 



VIII. Other Secretions. — Every one has heard at least 01 

 "pigeon's milk," and many are familiar with its administration to the 

 young birds. This is produced by both sexes for a week or so after 

 the hatching of the young, and is the result of a degeneration of the 

 cells lining the crop. Some of the cells break up, others are discharged 

 bodily. The result forms a milky emulsion-like fluid, which is regur- 

 gitated by the parents into the mouth of the young bird. A similar 

 substance is said to occur in some parrots. 



Of some interest, also, is the supra-salivation which occurs at the 

 breeding season in the swiftlets (Co//oca//a), which form the edible 

 birds' nests, — the costly, though to us wofully insipid, luxury oj 

 Chinese epicures. Certain salivary glands become peculiarly active 

 in these birds when breeding, and the secretion, which, according to 



* Merriam (Hayden's U. S. Geol. Survey, VI., p. 666) gives a definite 

 account of male lactation in Lepus bairdi. 



