MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 27i> 



comparing the energy of material actually oxidized in parallel experiments with and without 

 alcohol. The principles here involved may be explained as follows: 



77" energy needed and used by ilu body. — The body requires and uses a certain amount of 

 energy. This amount is larger when the man is at work and smaller when he is at rest, The 

 larger the amount of energy used, the more material will he metabolized to furnish it. If the 

 available nutrients of the food exceed the amounts metabolized, the excess will be stored in the 

 body. Assuming the store of carbohydrates to remain constant, the body will gain protein or 

 fat or both. Translating this last statement from terms of material to terms of energy, if the 

 available energy of the food exceeds the energy metabolized, the amount of energy in, the bod} 7 

 will be increased by the storage of energy in protein or fat. On the other hand, if the available 

 energy of the food does not supply the demand, the lack will be made up by drafts upon body 

 protein or fat. We thus have two measures of the energy used by the body. One is the gain or 

 loss of body protein and fat with a given amount of available energy in the food. The other is 

 the total energy metabolized whether it be more or less than the available energy of the food. 



Economy of 'utilization of 'energy '. — We have distinguished between the energy needed and 

 that actually metabolized. If the body uses the energy economically it does not metabolize more 

 than it needs. But it does not always make the most economical use of either material or energy. 

 If it has more food than it needs, it may use this wastefully. Part of the excess of material, at 

 times perhaps the whole, may be stored for future use, but often more or less of the excess is 

 simply consumed and the energy wasted. On the other hand, if the food only equals the demand, 

 and especially if it falls short and body material has to be drawn upon, the body will probably 

 make economical use of the energy of both food and body material. This was the case in the 

 experiments now under discussion. When the men were at rest the food supplied but little more, 

 and when they were at work it supplied less, than was actually needed. In these experiments, 

 therefore, the two measures just referred to, namely, the energy of body material gained or lost 

 and the total energy metabolized, show how much the body uses when the energy is economically 

 utilized. 



To state the case in another way, either the energy of material gained or lost with the given 

 diet, or the energy of the total material oxidized, gives a measure of the energy actually employed 

 for economical use. These quantities can be expressed in calories. 



Comparative economy of energy of different materials. — This brings us to the question at issue. 

 I- the energy of alcohol equal, superior, or inferior in value to that of carbohydrates or fats or 

 other nutrients of ordinary food as part of a diet for rest or for muscular work? Will a calorie 

 of energy from alcohol go as far. farther. 01 not as far as a calorie from sugar, starch, fat, or 

 protein in meeting the actual needs of the body ' The answer is to be sought in the experiments 

 in which a diet of ordinary food is compared with a diet containing alcohol, the total available 

 protein and energy of the food and the other conditions being the same in both experiments. 

 The test will be found in the gains or losses of body protein and fat, and in the total energy 

 metabolized in the two experiments. Any differences in either of these factors, to wit. (1) gains 

 or losses of body material, or (2) energy metabolized, provided they are outside the limits 

 of experimental error, must be attributed to the diet; that is to say, the alcohol in the diet. If 

 the body gains or loses the same amount of material, or if it metabolizes the same amount of 

 energy with both diets, a calorie of energy from one is equal to a calorie of energy from the 

 other, and as a source of energy the alcohol is equal to the isodynamic amount of the carbohy- 

 drates or fats which it replaces. If the gain of material is less or the loss-more, or if the total 

 energy metabolized is larger with the alcohol, the latter is inferior as a source of energy, and 

 vice versa. 



Experimental results. — Table L7 shows the differences between the available energy of the 

 food in experiments with and without alcohol and the corresponding differences between the 

 energy of body material gained or lost in the same experiments. The figures in the fourth and 

 sixth columns are computed from those in the third and fifth, respectively, using the factor 5.65 

 for the energy of one gram of protein, aud t».5i for that of one gram of fat. 



