MILK AND MILK-PREPARATIONS. 419 



The evacuation of milk (from 500 to 1500 cu. cm. in twenty-four hours) is 

 due not alone to the purely mechanical act of suction, but also to the functional 

 activity of the mammary gland. The latter consists primarily in erection of the 

 nipple, the smooth muscle-fibers of which exerting pressure on the sinuses of the 

 ducts, so that the milk may spurt forth in a stream. Moreover, the glandular 

 structure itself is reflexly stimulated to more active secretion through irritation 

 of the sensory nerves of the nipple. 



From the suddenly dilated glandular vessels a transudate pours abundantly 

 into the gland, by which, admixed with the milk-corpuscles and transformed into 

 milk, it is discharged. The amount of the secretion depends thus upon the degree 

 of blood-pressure. Accordingly, not only the milk stored up in the breast is sucked 

 out, but during the process of suction secretion is accelerated. "The breast is 

 willing, ' ' as the nursing women say. Only in this manner can be explained the speedy 

 arrest of the secretion of milk in connection with sudden emotional excitement .which 

 (as anger, fright, etc.) acts, as is known from experience, on the vasomotor nerves. 

 Laffont saw, following stimulation of the mammary nerve of a bitch, erection of 

 the nipples, dilatation of the vessels and secretion of milk. After section of the 

 external spermatic nerve in goats, Eckhard noted absence of erection of the 

 dugs, although the formation of milk suffered no interruption, which appeared 

 only after section of the nerves on both sides. Continued stimulation of sensory 

 nerves diminishes the secretion. The rarely observed condition of galactorrhea 

 is perhaps to be considered as a sort of paralytic secretion similar to the analogous 

 secretion of saliva. Heidenhain and Partsch noted increased secretion in dogs 

 when, following section of the glandular nerves, strychnin or curare was in- 

 jected. Atropin decreases the amount of milk. 



The slight milk-fever appearing with the commencement of the secretion of 

 milk is probably due to increased stimulation of the vasomotors, whose activity 

 must further be considered in relation with the transposition of the mass of blood 

 out of the pelvic cavity after birth. 



MILK AND MILK-PREPARATIONS. 



Milk must be designated a complete food, in which all of the constitu- 

 ents are present in such proportion that the body can thrive upon it. Ac- 

 cording to Johannessen the proportions in human milk are as follows: Albumin 

 i, fat 2, sugar 4.2; in cow's milk: albumin i, fat i, sugar 1.43. Of the milk 

 relatively more fat is absorbed in the intestine than albuminates. Human milk 

 is utilized up to 91.6 per cent., cow's milk to 90 per cent. 



Milk is opaque, bluish white, with a sweetish taste and a characteristic odor, 

 probably due to peculiar odoriferous bodies in the cutaneous secretion of the 

 gland. It has a specific gravity of from 1.030 to 1.032. On standing numerous 

 butter- globules collect on the surface as cream, beneath which is a watery bluish 

 layer. Human milk has always an alkaline reaction; cow's milk is at times alka- 

 line, sometimes acid, t and sometimes amphoteric. The milk of carnivora is 

 always acid. 



Milk consists of the fluid (milk-plasma, plasma lactis) and the morphological 

 constituents suspended in it, among which the milk-globules predominate. If the 

 milk be clotted, the cheese-cake (placenta lactis), which consists of coagulated 

 casein, containing milk-globules, separates from the whey (serum lactis). The 

 latter contains some dissolved albumin, milk-sugar and most of the salts. 



Milk-globules or Butter-globules. Microscopically, milk contains innumerable 

 small globules (Fig. 137). Colostrum-corpuscles and epithelium from the milk- 

 ducts are not common in mature milk. The milk-globules and the swollen casein 

 cause, on account of the reflection of light, the white color and the opacity of 

 milk. The milk-corpuscles consist of butter-fat and are apparently surrounded 

 by a thin layer of casein (haptogenic membrane) . 



That the milk-corpuscles are actually surrounded by a capsule of casein has 

 lately been definitely denied. Formerly, the following observations were offered 

 in support of the presence of the capsule: if acetic acid, which dissolves the casein- 

 capsule, be added to a microscopic preparation, the milk-globules run together 

 in fat-droplets. Further, if cow's milk be shaken with potassium hydroxid, 

 which destroys the casein-capsule, and then be mixed with ether, the milk becomes 

 clear and transparent, as the ether dissolves all of the fat-granules. Previously 

 to the treatment with potassium hydroxid or acetic acid, the ether is incapable 

 of setting free the fat in cow's milk from its capsule; in the case of human milk 

 the addition of ether and shaking alone suffice. Other investigators, however, 



