906 NUTRITION AND HEAT REGULATION. 



that they act as catalysts or hormones, or that they furnish some 

 essential constituents in the composition of living matter, or that 

 they exert a special influence upon some of the glands of internal 

 secretion. A significant fact, perhaps, in this connection is the 

 difference in result between total starvation and a diet adequate 

 from the energy standpoint, but deficient in vitamins. In the 

 former case there is deprivation both of energy material and of 

 vitamins, and while such animals lose in weight and eventually 

 die, they do not exhibit the lesions that are described. for animals 

 plentifully supplied with food, but deprived of vitamins. This 

 fact would seem to indicate that the vitamins are connected in 

 some way with the normal metabolism of the proteins, fats, and 

 carbohydrates taken into the body as foodstuffs. 



The Specific Djmamic 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. 



