576 



THE ANIMAL BODY AS A MACHINE 



containing carbohydrates could thus be compared with that experienced 

 on the diet containing fats, and the relative value of these constituents 

 of the dietary as tissue-sparers could thus be estimated. The external 

 Mechanical Work performed in both sets of experiments was as nearly 

 as possible the same, and equivalence of total energy-consumption on 

 the two diets would therefore indicate equal availability of fats and of 

 carbohydrates for the performance of mechanical work. The following 

 table summarizes .the results of these experiments: 



The substantial equivalence of the fats and carbohydrates as sources 

 of heat and work and sparers of tissue in these experiments is evident. 

 There is some indication that the loss of tissue on the fat-diet is greater 

 than it is on a carbohydrate-diet, and this is especially evident in the 

 experiment in which the total calorific value of the diet was relatively 

 high. The reason for this probably lies in the fact that, as Zeller has 

 recently shown, if the preponderance of fat over carbohydrates in the 

 diet be too great, even when the total calorific value of the diet is kept 

 constant, acetone bodies appear in the urine and an Acidosis arises 

 necessitating the production of Ammonia by the tissues tc neutralize 

 the excess of acid radicals in the blood. The output of nitrogen is 

 consequently increased and loss of body-substance accelerated. This 

 effect only appears in normal individuals, however, when less than ten 

 per cent, of the total calories are given in the form of carbohydrate. 

 Up to this limit, therefore, the carbohydrates in the diet may be replaced 

 by fat without influencing very appreciably the total heat-output or 

 wastage of tissue-materials. In Diabetes, of course, the limit of toler- 

 ance for fats is much lower than this. 



In the replacement of the fats by carbohydrates we are limited in 

 another direction. So far as the mere question of heat-equivalence 

 is concerned the complete replacement of the fats in the dietary by 

 carbohydrates is doubtless entirely feasible, more especially since the 

 conversion of carbohydrates into body-fat is a regular concomitant of 



