432 THE HUMAN BODY 



present. From rice hulls has been prepared a relatively simple 

 extract which has the curative properties of the entire hulls. The 

 explanation seems to be that certain organic substances are essen- 

 tial to normal metabolism. They are present in most foods, but 

 are wanting from some. When the diet is restricted to these 

 latter nutritional disturbances arise. A third dietary disease, 

 pellagra, appears to be due to a diet composed too largely of the 

 products of maize, grits, hominy, and cornmeal. For the sub- 

 stance or substances thus essential the name vitamines has been 

 proposed. We have no definite knowledge as to their mode of 

 action, although the suggestion has been made that they may 

 either act directly as hormones, or may be essential constituents of 

 some or all of the hormones manufactured in the Body. 



Recently the interesting discovery has been made that growth 

 of young animals is much favored by the presence in the diet of 

 certain unpurified fats, notably the fat of milk (butter fat), of egg 

 yolk, or of the liver (cod liver oil). Fats of exactly the same chem- 

 ical composition as these but from other sources, or these same 

 fats after careful purification, do not show this growth-favoring 

 property. The conclusion is that a vitamine-like substance is 

 present with these particular fats, and that the effect observed is 

 due to it. 



Occurrence of Occasional Accessories in Food. Variety in the 

 diet depends practically altogether upon the occasional accessories, 

 for the primary food stuffs are few in number and for the most 

 part without very pronounced tastes or flavors, with the single 

 exception of sugar, whose sweet taste makes it, to the eyes of 

 most children at least, the most desirable of all foods. To civilized 

 man variety of diet is a virtual necessity; the accessories, there- 

 fore, are to him of great importance. Both meats and vegetables 

 owe their characteristic flavors, in the main, to organic substances 

 present in them. We do not, however, depend wholly on these 

 substances for securing the needed variety in our food. Condi- 

 ments, pepper and mustard for example, and spices are used very 

 largely in all civilized countries. Chocolate, coffee, and tea are 

 taken by most people more for their agreeable flavor than for their 

 stimulating properties. 



The Nutrients. The actual nourishment of the Body depends, 

 as stated above, primarily upon the taking of sufficient quantities 



