278 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



the rest of the heat. If the muscular energy is the first product of the transformation of 

 potential energy, it is conceivable that there might be some attribute of alcohol which would 

 prevent its potential energy from being changed into mechanical energy. But there is nothing 

 in the results of experiment to imply any such difference between alcohol on the one hand, and 

 sugar, starch, or fat on the other. The case regarding the transformation of energy is like that 

 just referred to regarding the use of the energy after it is transformed. There is no evidence 

 of any difference between alcohol and other nutrients in either respect, but there is no proof that 

 the difference does not exist. 



The most satisfactory method of study of this question as to whether alcohol can be a source 

 of the mechanical energy exerted by the muscles is by measuring the amounts of different 

 substances metabolized and the amounts of muscular work done, and thus getting light upon the 

 comparative efficiency of the several substances as parts of a diet for muscular work. 



If the experiment could be made with lean meat and alcohol in such a way that the body 

 could obtain no other fuel than alcohol and protein, and the energy of the internal and 

 external muscular work should be found to exceed that of the protein, it would be clear that 

 the rest of the muscular energy must come from the alcohol. But as yet we have no means for 

 measuring the internal work, and it would probably be difficult to find a man who could do 

 much external work day after day on such a diet without drawing upon the store of material 

 in his body. 



For the present, therefore, we are limited to experiments in which other fuel is burned with 

 the alcohol, and our conclusions must depend upon measurements of (1) the energy supplied In- 

 each kind of fuel, (2) the energy given off from the body, and (3) the amount of muscular work 

 performed. 



Here again we meet a difficulty, namely, that of measuring the muscular work. We have 

 to do with two kinds of work, external and internal. The external work is that which is 

 performed outside of the body, as, for instance, the power which a man riding a bicycle applies 

 to the pedals. This is capable of quite accurate measurement. Such measurements were made in 

 the experiments here described. By internal work is meant that of circulation, respiration, 

 digestion, etc. Thus a not inconsiderable amount of energy must be used for the muscular 

 contractions of the heart by which the blood is pumped out through the arteries and back from 

 the veins. It is held by some physiologists that a large portion of the total energy supplied by 

 the food is used for this internal physiological work. At present no exact method is known for 

 measuring the internal work of the body. It is transformed into heat before it leaves the body 

 and in the experiments with the respiration calorimeter it is collected and measured as part of 

 the total heat given off. But this total heat includes also the heat which was produced in the 

 body and not used for muscular work, and no way has yet been found to distinguish between the 

 heat which has and that which has not been used, and to measure the two quantities of heat 

 separately. 



We know from measurements of the external muscular work that it represents at most a 

 fraction, and generally a small fraction of the total energy transformed. It may be that in the 

 case of a man doing a large amount of muscular labor this external work added to the internal 

 work would account for the larger part of the total energy transformed in the body. 



The measurements of income of energy from the oxidation of ordinary nutrients and alcohol 

 and of outgo of energy in the different forms of heat and external muscular work therefore do 

 not answer the specific question as to how much of the energy provided by the alcohol is used 

 for either internal or external muscular work, or both. 



Economy of utilization of th energy of tht rations with mn! without alcohol. — We may 

 nevertheless get some light on the question by putting it in another way: Is the total energy 

 of the ration used as economically when part of it is supplied by alcohol as when the whole comes 

 from ordinary food? The question may be approached in two ways. (1) by considering the 

 differences in the amounts of available energy in the diets with and without alcohol, and compar- 

 ing these, with the energy in the body protein and fat gained or lost in the two cases, and (2) by 



