478 



VICTOR C. MYERS 



limits of normal variation in the constituents of human and cow's railk 

 from the beginning of the second mouth of lactation onward, the figures 

 representing percentages of whole milk: 



It is apparent that human milk contains less protein but more sugar than 

 cow's milk. The protein of human milk differs from that of cow's milk 

 in one very important respect, quite aside from the total quantity of 

 protein. It contains much less casein but rather more lactalburnin. Ac- 

 cording to Meigs and Marsh, both human and cow's milk contain im- 

 portant non-nitrogenous substances of an unknown character. Early 

 human milk contains about 1 per cent of these unknown substances ; milk 

 from the middle period of lactation about 0.5 per cent Cow's milk from 

 the middle period of lactation contains about 0.3 per cent of the unknown 

 substance. 



Denis, Talbot and Minot have studied the nonprotein nitrogenous 

 constituents of human milk. They summarize the results of the examina- 

 tion of 71 samples as follows : 



. to 100 c.c. 



In some of the cases the nonprotein and urea nitrogen were also deter- 

 mined in the blood and practically the same figures obtained as in the milk. 



In a series of about forty cases Denis and Minot (c) found the choles- 

 terol content of human milk to vary from 10 to 30 mg. per 100 c.c*, figures 

 of 10 to 20 mg. being obtained chiefly in milk with a low fat content and 

 figures of 20 to 30 mg. with a high fat content. According to Boswortb 

 r*nd ^ r an Slyke, cow's milk contains 0.052 per cent of potassium citrate 

 and 0.222 per cent of the sodium salt, while in human milk the potassium 

 salt, 0.103 per cent, is in excess of the sodium salt, 0.055 per cent. Sommer 

 and Hart have shown that the citric acid of cow's milk (0.2 per cent) 

 is not destroyed or changed on heating. 



The mineral content of milk is of great interest and importance. 

 Holt, Courtney and Fales(&) have given the average composition of the 



