38 PHYSIOLOGY AND NATIONAL NEEDS 



and especially of the cortex or embryo of the wheat ; 

 or, as it is interesting to know, of the " polishings" 

 which are removed when rice is milled. A substance 

 soluble in water, and that in small quantity, is all 

 that is necessary to convert the, by itself, useless 

 diet into a useful one. Suppose, however, that 

 instead of an animal fat, we have supplied in the 

 original mixture a pure vegetable fat. Then the 

 addition of the just- mentioned watery extracts, 

 alone, may be quite ineffective — they fail to make 

 the dietary one which will sustain the animal. Re- 

 place, however, the vegetable fat with butter once 

 more, and, given the watery extract, the animal will 

 thrive. Now, the vegetable fat is a perfectly good 

 food. As fat, as serving the special purpose of 

 fat itself in the body, there is no reason to doubt 

 that it is as good as animal fat. But it lacks some 

 constituent which the latter contains, though that 

 something is once more present in very small 

 amounts. It will be seen at once to what this evi- 

 dence tends. There are at least two vitamines of 

 importance to nutrition, one associated with certain 

 fats and one soluble in water. Both must be present 

 in sufficient amount in any dietary providing proper 

 nutrition. Following American suggestion, we now 

 speak of them respectively as the '' Fat-soluble A " 

 and the " Water-soluble B." 



The table shows the relative distribution of these 

 two substances in certain natural products, the 



