CH. XXX.] MILK 481 



any unusual strain, such as privation or a severe illness, would then 

 find us without any reserve of nutrient energy, and we should 

 probably suffer more severely in consequence. The poor around us 

 have had nolens volens to subsist on a Chittenden diet for years, 

 whereas Chittenden's experiments only lasted months, and nearly all 

 of his subjects have returned now to their previous diet. The 

 underfed condition of the poor is apparent, and is not such as to 

 make others inclined to follow their example. In countries like 

 India, where the vegetarian native population is diluted with the 

 meat-eating white races, it is the former who more readily succumb 

 to the effects of disease. The recent development of the Japanese 

 is by some attributed in part to the fact that they are accustoming 

 themselves to a richer nitrogenous diet than they took in the past. 



It is doubtful if the minimum is also the optimum. We take in 

 protein, and rapidly eliminate most of its nitrogen as urea, without 

 building it up first into the body tissues ; but some is wanted by the 

 body tissues to repair their waste, and some of the cleavage products 

 of the food-protein are especially necessary for the synthesis of tissue 

 protein ; it is in order to obtain a sufficient quantity of these 

 scanty cleavage products that we ingest what at first sight is an 

 excess of the proteins which yield them. But after our study of 

 digestion and excretion, we shall be in a better position to discuss 

 this question more fully, and we shall return to it in the chapter 

 on Metabolism. 



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 protein 

 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 

 FIG. ass. Globules of cow's milk, x 400. 0'0015 to 0*005 millimetre (fig. 338). 



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 



2 11 



