248 FOOD INGESTION AND ENERGY TRANSFORMATIONS. 



basal requirement of a period of 5 to 6 hours, during which time we 

 may properly say the conditions are those of excessive carbohydrate 

 feeding. Just what is meant by excessive carbohydrate feeding is, 

 of course, in large part dependent upon the period between the feedings 

 and the total amount ingested, but logically there is no reason why 

 the above argument is not sound. It is fair to assume, therefore, that 

 part of the carbon-dioxide may be derived from the cleavage of carbo- 

 hydrate to form fat. 



Third, an increased carbon-dioxide excretion may result from an 

 actual increase in metabolism, during which process additional carbona- 

 ceous material is burned, with a resultant increase in the production 

 of carbon dioxide. This fact is of prime importance, since the measure- 

 ment of oxygen consumption, and particularly of heat production, will 

 likewise indicate such an increase in metabolism. 



If only the carbon-dioxide excretion is measured, it is impossible 

 even to estimate the varying amounts due to each one of these three 

 factors. On the other hand, when the oxygen consumption or heat pro- 

 duction is determined, we have definite information as to the probable 

 amount of excess carbon dioxide due to an increase in metabolism. 

 The fact has already been clearly established by direct calorimetry, 

 and is substantiated by indirect calorimetry, that the ingestion of car- 

 bohydrate in these experiments actually results in an increased heat 

 production, that is, an increased metabolism entirely aside from inter- 

 mediary transformations. Indeed, the heat production, as indicated 

 in the data for the calorimeter experiments, is of such a magnitude as 

 completely to preclude the assumption that the extra heat produced 

 is due solely to hydration or simple cleavage. We may therefore 

 properly consider that the ingestion of carbohydrate, particularly of 

 sucrose and levulose, results in a direct stimulus to the total metabolism 

 in the body. 



The marked rise in the respiratory quotient also leads to the firm con- 

 viction that the fat combustion must, in large part, have been replaced 

 by carbohydrate metabolism, at least in those experiments in which the 

 respiratory quotient closely approaches unity. With respiratory quo- 

 tients of 0.97, which by correction would result in non-respiratory 

 quotients of unity, we may likewise assume that the non-protein 

 metabolism is due to carbohydrate, an assumption which seems legiti- 

 mate in view of the fact that quotients of this character frequently 

 appear in our series. On the other hand, quotients considerably 

 above unity also frequently appear, especially in the levulose and 

 sucrose experiments. These distinctly imply, if not absolutely prove, 

 the formation of fat from carbohydrate. It still remains a question 

 as to whether this latter process, namely, the formation of fat from 

 carbohydrate, may not proceed even when there is a somewhat lower 

 respiratory quotient than that of unity. With the marked differences 

 in the action of the several sugars on the total metabolism, and par- 



