MILK 



333 



of the action of rennin upon this protein. The confusion of terms 

 may be represented thus: 



English. German. 



Caseinogen. = Casein. 



Casein. = Paracasein. 



The most important difference between human milk and cow's 

 milk is in the protein content, although there are also differences in the 

 carbohydrate and ash and likewise striking biological differences diffi- 

 cult to define chemically. It has been shown that the casein of human 

 milk differs from the casein of cow's milk in being more difficult to 

 precipitate by acid or coagulate by gastric rennin. The casein curd 

 (paracasein) also forms in much looser and more flocculent manner 

 than that from cow's milk and is for this reason much more easily 

 digested than the latter. (For illustrations of milk curds, see Figs. 105 

 to 1 08, page 332.) Both human and cow's milk contain important 

 non-nitrogenous substances of an unknown character. Human milk 

 contains the greater quantity of these substances. 1 



Non-protein nitrogen, urea and creatinine are present in normal 

 human milk in approximately the same concentration as in normal 

 human blood 2 (See Blood Analysis, p. 273). 



The relative composition of human and cow's milk is shown in the 

 following table which embraces data reported by Meigs and Marsh. 



COMPOSITION OF MILK (PER CENT OF WHOLE MILK) NORMAL VARIA- 

 TIONS FROM BEGINNING OF SECOND MONTH OF LACTATION 



The above data indicate that human milk contains less protein, 

 more sugar and much less ash than cow's milk. The percentage 



1 Meigs and Marsh: Jour. Biol. Chem., 16, 147, 1913. 



8 Denis, Talbot and Minot; Jour. Biol. Chem., 39, 47, 1919. 



* Protein starts high and decreases whereas sugar starts low and increases. 



