272 NORMAL PARTURITION. 



It is admitted that milk is due to a fatty degeneration of the 

 epithelial cells of the gland follicles, in which they are greatly multiplied 

 and developed during lactation. These cells rupture, and nothing 

 remains but the fat globules of the milk. 



But in the colostrum the epithelial cells have not undergone this 

 change ; their wall is intact, and they still contain their oil granules, 

 and consequently constitute the colostrum corpuscles. Colostrum, as 

 has been mentioned, is coagulable at a low temperature, and it may 

 be said that the albumin takes the place of casein ; but soon after 

 parturition the former disappears and the lacter is present. Towards 

 the end of lactation, however, if the animal is pregnant, the milk again 

 loses its casein, and becomes very albuminous; consequently, coagulable 

 by heat. Its sugar also diminishes or disappears altogether. The 

 leucocytes seem to be increased in number in the colostrum, when the 

 animal is disturbed or its health deranged ; and as the young creatures 

 are often attacked by diarrhoea, this is ascribed to the presence of these 

 particles. 



Milk. — Towards the fifth or sixth day, or even longer, after par- 



B 

 r9:}oy. 



r 



Fig. 80. 



Mammary Gland during Lactation. 



A, Lobule of the Mammary Gland filled with Cells ; B, Milk or Fat Globules ; 

 C, Colostrum, a, Cell filled with Fat Granules and with a visible Nucleus ; 

 b, Cells from which the Nucleus has disappeared. 



turition in the Cow and Mare, earlier with some of the other animals, 

 the colostrum disappears, and then we have the ordinary milk. This 

 is an opaque, pure white, or slightly yellowish fluid, possessing a sweet 

 taste, and a faint odour somewhat resembling that of the animal from 

 which it is obtained ; it is unctuous to the touch, has an average density 

 of 1032 to 1041, according to the species and other circumstances •} 

 and is composed of three essential parts — water, butter, and casein. 

 We have in addition albumin, milk-sugar, and mineral matters. 



The three principal constituents are easily separated— the fat or 

 cream by allowing the fluid to stand at rest for some time ; by pressure 

 the casein is separated in a solid mass ; and the remaining portion 

 contains the water. 



The milk varies considerably, as has been said, according to species, 

 breed, age, food, the period of lactation and milking, climate, state of 

 health, etc. In Herbivorous animals it is generally alkaline ; in Car- 

 nivorous, acid. 



1 Cow's milk of good quality, according to Voelcker, has a specific gravity of about 

 1030 ; Woman's milk, 1020 ; Goat's and Ewe's milk, 1035 ; Ass's milk, 1019, 



