50 FOOD INGESTION AND ENERGY TRANSFORMATIONS. 



degree of accuracy in the percentage increase obtained as a result of the 

 superimposed factor. 



Even when the basal value has been well established it does not 

 necessarily follow that the metabolism of an individual will remain 

 unchanged for an indefinite length of time, inasmuch as there will be 

 changes in the composition of the body, particularly gains or losses of 

 glycogen and fat; growth, climate, the season of the year, and such 

 factors as temperature environment and various stimuli to the body 

 may likewise have an effect upon metabolism. This question will be 

 considered more at length in the discussion of the various methods for 

 obtaining the basal metabolism. 



Of the numerous factors affecting muscle tonus and nerve stimu- 

 lation, great emaciation and the ravages of disease are distinctly of 

 pathological rather than of physiological significance. In a number 

 of pathological cases, when the metabolism is at a subnormal point 

 through muscular atrophy and similar causes, there may be even less 

 muscle tonus and minor muscular movement than with healthy per- 

 sons in profound sleep. But these abnormal conditions need not be 

 considered here. 



It may be of considerable moment in this connection to note whether 

 or not the increment above the base-line due to the ingestion of a defi- 

 nite amount of food is wholly independent of the absolute value of the 

 base-line. For example, we will assume that the taking of a certain 

 amount of food resulted in an increment of 25 calories during a period of 

 6 hours when the base-line was determined with the subject in complete 

 muscular repose, in the post-absorptive condition, and lying awake. 

 With the subject asleep, the base-line would unquestionably have been 

 somewhat lower than that obtained with the subject awake. Have we 

 any reason to believe that the increment due to the ingestion of food 

 will be affected by this difference in conditions? Unfortunately our 

 evidence is by no means clear on this point. 



The particular problem studied in this publication is the absolute 

 increase in the heat production caused by the ingestion of food. Aside 

 from disease, the two principal factors which contribute to the depres- 

 sion of the base-line are sleep and fasting. It is conceivable that with 

 a low base-line, such as would be found in deep sleep or during fasting, a 

 greater increment would be obtained with a definite amount of food 

 than with a higher base-line. On the other hand, it is possible that 

 during sleep, and especially with a condition of under-nutrition resulting 

 from fasting, the cells may be less susceptible to stimuli. In such a case 

 the increment in the metabolism would obviously be less than when 

 the subject is awake and in a normal state of nutrition. 



Experiments primarily measuring the output of heat resulting from 

 a definite amount of muscular work have shown that if the basal value 



