914 NUTRITION AND HEAT REGULATION. 



rice furnishes its quota of carbohydrate (and protein) for the 

 energy needs of the body. According to this conception- a diet 

 made up mainly or exclusively of polished rice may be adequate 

 from an energy standpoint, but nevertheless deficient in some un- 

 known particular. Beriberi or polyneuritis constitutes, therefore, 

 what is known as a deficiency disease. The second accessory, the 

 fat-soluble A, is equally important. In our natural foods it is found 

 chiefly in animal fats, particularly butter-fat and the fat of the egg- 

 yolk, and in the foliage of plants. The usual grains in cereals con- 

 tain insufficient amounts of this accessory, but it occurs in larger 

 quantity in the leaves, in alfalfa, for example, cabbage, etc. Young 

 rats fed upon a diet of purified protein, starch and lard, and the 

 proper quota of inorganic salts do not grow normally, but if butter- 

 fat is added normal growth takes place. Chemical examination 

 of this fat-soluble accessory indicates that it is lacking in nitrogen 

 and phosphorus, so that as far as it is concerned the term "vitamine" 

 as a group name is inappropriate. As stated above, feeding experi- 

 ments indicate that both of these accessory substances are essential 

 to normal growth and maintenance. The part that they play in 

 normal metabolism is at present entirely unknown. Since only 

 very small amounts are needed in the daily diet, it has been sug- 

 gested (Mendel) that they act after the manner of hormones. 



The Specific Dynamic Action of Proteins. This somewhat 

 indefinite term is used by Rubner to designate the fact that pro- 

 tein foods seem to increase the metabolic processes of the body 

 to a greater extent than the fats or carbohydrates. This pecu- 

 liarity may be demonstrated, for instance, in the case of an animal 

 that has been starved (eighteen hours) until the gastro-intestinal 

 tract is free from food. * If the heat- production of such an ani- 

 mal is determined at hourly periods, it gives an index of what may 

 be called its basal metabolism when living on the material within 

 its body. If in this condition the animal is fed with carbohydrate 

 (glucose) there will be an increase in heat production, lasting for 

 three or four hours, which may amount to as much as 30 to 40 

 per cent. Feeding with meat or with some of the amino-acids 

 (glycin, alanin) causes a similar but more marked increase in 

 metabolism. After a large diet of meat the increase may amount 

 to as much as 90 per cent. This effect upon the metabolism is 

 exhibited especially by proteins. Many explanations of it have 

 been proposed, but recent experiments indicate that it is probably 

 due to some direct stimulating action of the intermediary acids, 

 such as lactic or pyruvic acid, which are formed during the further 

 metabolism of the amino-acids in the body. This stimulating 

 effect of proteins may furnish a physiological explanation of the 

 fact that in hot summer weather it is advisable to avoid a meat diet. 



* See Lusk, "Jour, of the Amer. Med. Association," September 5, 1914. 



