MILK FROM MAMMALS OTHER THAN THE COW 



Human Milk. In previous chapters frequent reference has 

 been made to human milk, and little more need be added. As 

 a rule, human milk is more yellowish than cow's milk and has 

 a sweeter taste, owing to a larger content of milk-sugar. The fat 

 globules are larger than those of the milk of most cows, but 

 fewer in number. The size of the fat globules varies from 0.9 

 to 32 microns. The fat rises within a few hours after 'drawing 

 and separates more completely than the fat in cow's milk. There- 

 fore, human skimmed milk is more transparent than cow's milk. 

 Human cream is decidedly yellow in color. 



Coagulation of the casein is produced with some difficulty. 

 By adding dilute acetic acid to diluted skimmed milk at 40 C. 

 a fine flaky precipitate is formed which does not settle, but rises 

 to the surface. Rennet coagulation is not apparent to the naked 

 eye unless acid is added. By rennet coagulation human casein 

 is split into paracasein and a soluble albumin, similar to the split- 

 ting of cow casein by rennet. Pure human casein is soluble in 

 weak alkalies, but the solution has a yellowish in place pf the 

 bluish tint of cow casein. 



Bosworth and Giblin found that the valency of human casein 

 is 8 and its molecular weight 8888. The valency of human para- 

 casein is 4 and its molecular weight 4444. The same authors 

 state that human casein resembles bovine and goat casein in sev- 

 eral respects. These caseins have the same nitrogen, phosphorus, 

 and sulphur content; they have the same 'valency and form the 

 same salts with bases; they have the same molecular weight; 

 they are acted upon by rennet in the same manner; and the para- 

 casein resulting frcim action upon human casein is similar to that 

 of cow's milk. 



Fresh human milk is slightly acid to phenolphthalein and 

 alkaline to litmus. It sours and coagulates spontaneously. Ham- 

 marsten gives the freezing-point of human milk at 0.589 C. The 

 specific gravity of the fat is 0.966 at 15 C. It melts at 34 C. 

 and solidifies at 20.2 C. 



The same author states that human milk is coagulated by gas- 

 tric juice, but subsequently dissolves in it readily. Human milk 

 is richer in lecithin than cow's milk, but the latter contains more 

 phosphorus than human milk because of its higher casein content. 



The ash of human milk varies between 0.19 and 0.34 per 

 cent., which is considerably less than that of cow's milk. Trunz 



654 



