46 FOOD INGESTJON AND ENERGY TRANSFORMATIONS. 



legless man and for an achondroplastic dwarf with very small arms and 

 legs and normal trunk than for three normal controls of greater weight 

 and greater surface area. They accordingly conclude that the inten- 

 sity of the specific dynamic action is not proportional to the mass of 

 the musculature, and suggest that it may be due to a greater concen- 

 tration of amino-acids in the blood flowing to the muscles or to the 

 presence of a liver which, in proportion to the size of the organism, is 

 relatively larger than the normal. 



SUMMARY OF PREVIOUS INVESTIGATIONS. 



In spite of the wide variations observed in the increase of the metab- 

 olism with different foodstuffs, there is a distinct uniformity in the 

 majority of experiments which indicates that the act of taking food 

 results in an increased heat production, carbon-dioxide production, and 

 oxygen consumption. With diets predominating in carbohydrates, 

 the quantitative relationship of these increases is more strikingly 

 noticed in the carbon-dioxide production. With the protein diets, the 

 evidence is more pronounced with the oxygen consumption. With the 

 three typical nutrients we may consider as firmly established: (1) that 

 the ingestion of a diet rich in protein results in a marked increase in 

 the total metabolism both for the oxygen consumption and the carbon- 

 dioxide production, this increase being, in general, roughly proportional 

 to the amount of protein ingested ; and (2) that with carbohydrate there 

 is almost invariably a marked increase in the excretion of carbon diox- 

 ide, and in many instances, especially with sugars other than dextrose, 

 there is likewise an increase in the oxygen consumption. The exact 

 interpretation of the increases with carbohydrate is not so simple as 

 in the case of protein, for there is undoubtedly a formation of fat from 

 carbohydrate. In respiration experiments in which only the carbon- 

 dioxide production is determined, the interpretation of the increase is 

 obviously very difficult. With a fat diet, the evidence is conflicting and 

 little information is obtainable. Pure fat is rarely given in experi- 

 ments, but is usually combined with other food materials. In those 

 instances in which it has been included in a mixed diet, a small increase 

 has usually been noted. Two of three experiments made by Gigon 

 with pure olive oil implied a distinct lowering of the basal metabolism. 

 In any event, it is safe to conclude that the influence of the ingestion of 

 fat upon metabolism is very small compared with that of sugar and 

 protein. 



Although a considerable portion of the literature is devoted to a dis- 

 cussion of the causes of these variations in the metabolism, the two 

 main theories have been (1) the Verdauungsarbeit theory of Zuntz and 

 his scholars, which ascribes the greater proportion of the increased 

 metabolism to the work of digestion, and (2) the specific dynamic 



