3 i6 



PHYSIOLOGICAL CHEMISTRY 



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. Both human and cow's milk contain im- 

 portant non-nitrogenous substances of an unknown character. Human 

 milk contains the greater quantity of these substances. 1 



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 VARIATIONS 

 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 

 composition of human milk at different periods is represented in the 

 following table. 2 



PERCENTAGE COMPOSITION OF HUMAN MILK BY PERIODS 



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



2 Holt, Courtney and Fales: Am. Jour. Dis. Children, 10, 229, 1915. 



