380 MANUAL OF PHYSIOLOGY. 



emulsion of fat, the suspended particles of which are kept from 

 running together by a superficial coating of dissolved casein. 

 When left at rest, the light, fatty particles float to the top and 

 form the cream. 



When the mammary glands commence to secrete, the milk 

 contains numerous peculiar structural elements which finally quite 

 disappear from the secretion, but which are of considerable in- 

 terest in relation to the physiological process of the secretion. 

 These are the colostrum corpuscles, which consist of large spheri- 

 cal masses of fine fat-globules held together by the remains of a 

 gland cell, which incloses the fat-globules as a kind of sac or 

 case, and in which at times a nucleus can be made out. 



The most remarkable point about the chemical composition of 

 milk as a secretion is the large proportion of proteid and fat it 

 contains. It appears that there are two distinct albuminous bodies 

 present, viz. : casein, which appears identical with alkali-albu- 

 min, and another form of albumin allied to serum-albumin. The 

 fats are present in the shape of globules of various sizes, being in 

 the condition of a perfect emulsion, as above stated. They con- 

 sist of glycerides of palmitic, stearic, and oleic acids. 



The milk-sugar is very like glucose or grape-sugar, but not so 

 soluble. It has the peculiarity of undergoing lactic fermentation. 



Of the inorganic constituents of milk the most important are 

 sodium chloride, and phosphates and carbonates of the alkalies ; 

 and it is a remarkable fact that the potash compounds, which are 

 the most abundant iii the red blood corpuscles, are present in 

 greater quantity than those of soda. 



The following table shows the composition of human milk, a 

 comparison of which with that of some domestic animals will be 

 found on page 94 : 



1000.00 



