CH. XXVIII.] 



MILK 



461 



There have been other experiments which show that even Euro- 

 peans can thrive on diets even scantier than this. But to most 

 English people Ranke's and Moleschott's diets would not appear to 

 err on the side of generosity. From the composition of the more 

 commonly used foods taken in fairly average amounts, G. K Stewart 

 calculates that 500 grammes of bread and 250 grammes of lean meat 

 constitute a fair quantity for a man fit for hard work. Adding 500 

 grammes of milk, 75 grammes of oatmeal porridge, 30 grammes of 

 butter, and 450 grammes of potatoes, we get, approximately, 20 

 grammes of nitrogen and 300 grammes of carbon contained in 135 

 grammes of proteid, 97 grammes of fat, and about 400 grammes of 

 carbohydrate. 



Milk. 



Milk, which we have already spoken of as a perfect food, is only 

 so for young children. For those who are older, it is so voluminous 

 that unpleasantly large quantities of 

 it would have to be taken in the 

 course of the day to ensure the proper 

 supply of nitrogen and carbon. More- 

 over, it is relatively too rich in proteid 

 and fat. It also contains too little 

 iron (Bunge): hence children weaned 

 late become anaemic. 



The microscope reveals that it con- 

 sists of two parts : a clear fluid and a 

 number of minute particles that float 

 in it. These consist of minute oil 

 globules, varying in diameter from 

 0-0015 to 0-005 millimetre (fig. 388). 



The milk secreted during the first 



few days of lactation is called colostrum. It contains very little 

 caseinogen, but large quantities of albumin and globulin instead. It 

 coagulates like white of egg when boiled. Microscopically, cells 

 from the acini of the mammary gland are seen, which contain fat 

 globules in their interior ; they are called colostrum corpuscles. 



Reaction and Specific Gravity. The reaction of fresh cow's 

 milk and of human milk is amphoteric ; that is, it turns blue litmus 

 red, and red litmus blue. This is due to the presence of both acid and 

 alkaline salts. All milk readily turns acid or sour as the result of 

 fermentative change, part of its lactose being transformed into lactic 

 acid. The specific gravity of milk is usually ascertained with the 

 hydrometer. That of normal cow's milk varies from 1028 to 1034. 

 When the milk is skimmed the specific gravity rises, owing to the 

 removal of the light constituent, the fat, to 1033 to 1037. In all 



FIG. 388. Globules of cow's milk, x 400. 



