900 THE EXTERNAL SECRETIONS 



the health of the woman. In this connection, it is also of interest to 

 note that the act of suckling excites tonic contractions of the uterus, a 

 means commonly employed to cause this organ to assume its former 

 shape after labor, and especially when this involution is slow and is 

 associated with hemorrhage. It should also be noted that the secre- 

 tion of milk is not exclusively a function of the pregnant female, 

 because many cases are on record of men and boys possessing well 

 developed and actively secreting mammae. It had also been observed 

 that virgin bitches may produce milk and that sterile mules may 

 yield sufficient milk to suckle a foal. 



Properties of Milk. When the mammsB first begin to discharge 

 their secretion, they do not yield pure milk but a peculiar fluid which 

 is known as colostrum. A few drops of this secretion may usually be 

 obtained within a short time after the completion of labor by gently 

 massaging the breasts in the direction of the nipples. Its total amount, 

 however, is never considerable although it flows more freely later on. 

 As has been stated above, this material is gradually flushed out of the 

 ducts, giving way in the course of two or three days to pure milk. 

 To begin with, the colostrum appears as drops of a watery and usually 

 very cloudy fluid, possessing a specific gravity of 1.040 to 1.080. In 

 larger quantities it exhibits an opalescent, yellowish appearance, and 

 gives rise to a coagulum of similar color. The pigment to which the 

 latter is due, is contained in its fatty admixtures. When examined 

 under the microscpoe, it is seen to contain numerous fat-globules and 

 fragmented cells, among which are many leukocytes which have 

 migrated and have become loaded with fat-droplets. Colostrum 

 yields little or no casein but about 3 per cent, of proteins, consisting 

 of coagulable lactalbumin and lactoglobulin. Moreover, while it con- 

 tains as much fat as the pure milk secreted subsequently, it embraces 

 somewhat greater quantities of lactose and salts. Colostrum is na- 

 ture's laxative, and hence, the infant should be allowed to partake of 

 it freely. 



The milk, following the colostrum, is an opaque fluid, possessing a yellowish 

 white or bluish white appearance according to its concentration. It possesses a 

 sweetish taste and a very characteristic odor. Its specific gravity varies between 

 1.026 and 1.036, the highest values being generally obtained only in well nour- 

 ished women. It is neutral to litmus, alkaline to lacmoid, and acid to phenol- 

 phthalein. When examined under the microscope, it is seen to consist of a watery 

 part, or milk-plasma and numerous fat-globules, or milk-corpuscles. The diameter 

 of the latter varies between lju and 6/t. Here and there we also recognize 

 fragmented epithelial cells, leukocytes and nuclear material. Milk, therefore, is 

 essentially an emulsion of fat, the opaque appearance of which is due to the diffuse 

 reflection of the light by these globules. On standing, these droplets of fat rise 

 to the surface, owing to their lesser specific gravity, and form the cream. By 

 mechanical agitation the latter may be made to coalesce to form butter. This fact, 

 that it requires agitation to coalesce the fat-globules, has been the subject of much 

 study. Thus, it has been shown that the globules in cow's milk are invested 

 by a mucous-like envelope, which must first be broken up before the fat can run 

 together. In addition, it has been assumed that the globules in other types of milk 

 are surrounded by a haptogen membrane which is formed of the proteins of the 



