THE ABSORPTION AND USE OF FOODS 509 



strain upon these organs, and if it does tend to throw upon them 

 excessive labor it is clear that the consumption of proteins ought 

 on this account to be kept as low as possible. The idea that the 

 excretory organs are endangered by ordinary amounts of protein 

 in the diet is not sustained by any very convincing evidence. In 

 fact there is at least one race of men, the Eskimos, in which huge 

 consumption of flesh proteins is the rule and in which no tend- 

 ency to gout and the other diseases ordinarily attributed to over- 

 use of meat is discoverable. 



In the matter of cost, which must also be taken into considera- 

 tion, carbohydrates have a marked advantage over the other 

 food stuffs. For example, bread, which is chiefly carbohydrate, 

 yields, dollar for dollar, about ten times as many Calories as lean 

 beef, a protein. The cheapest proteins are the vegetable ones; a 

 given weight of protein costing about five times as much when 

 bought as beef as when purchased in the form of beans. 



Still another factor to be taken into account is the appetizing 

 quality of the different foods. The dependence of the whole di- 

 gestive process upon a proper initial psychic secretion of gastric 

 juice emphasizes the importance of the use of appetizing foods. 

 Boiled meat contains as much nourishment as the same weight 

 of roasted meat, but the former is less desirable as a food because 

 the process of boiling extracts from it the substances which impart 

 to meat its flavor. Eggs are exceedingly nutritious, but to some 

 people they are practically valueless as food, because they inspire 

 aversion rather than appetite. 



The Specific Dynamic Action of Proteins. A feature of protein 

 metabolism that is both interesting and of great dietary impor- 

 tance is a stimulating power it exercises toward the whole meta- 

 bolic process. Whenever in the Body active consumption of 

 proteins is going on there occurs, in addition to the metabolism 

 of the proteins themselves a further metabolism of some of the 

 reserve fuel supply of the Body, with, of course, a corresponding 

 increase in the total heat production. This stimulating property 

 of protein has been called its specific dynamic action. Practically 

 it is important in regulating the heat production at different sea- 

 sons of the year. In winter, when we naturally eat protein freely, a 

 large amount of heat is necessary to maintain the Bodily warmth. 

 In summer, when we wish to produce no more heat within our 



