518 NUTRITION. 



heat-units. The heat-value, then, represented by the formation of 12-56 ounces of water 

 would be 5,432-2 heat-units. 



During these five days, the subject of this experiment walked 317i miles and lost 55'2 

 ounces in weight. We calculated for these five days the total heat produced by the body, 

 and the heat-units used in maintaining circulation and respiration and in walking 317-J 

 miles. We then calculated the heat-value of the food and of the loss of body-weight, 

 the latter estimated as muscular tissue, taking no account of the hydrogen. According 

 to this, there remained 38,926-52 heat-units unaccounted for. If we take in addition the 

 heat-value represented by the excess of water discharged for tbe five days, which is equal 

 to 27,161-00 heat-units, we have 11,765-52 heat-units unaccounted for, which is about 

 sixteen per cent, of the heat-units expended, instead of fifty-five per cent. However, in 

 estimating the heat-units used in respiration, circulation, and walking 317& miles, we 

 took calculations that we regard as grossly erroneous and use them for sake of argument 

 and without any confidence in their accuracy. The percentage of sixteen is probably 

 not more than the error in the computation of the heat-units converted into force ex- 

 pended in maintaining circulation and respiration and in walking 317$ miles. 



One of the observations, in which we calculated the amount of water discharged as 

 compared with the quantity ingested, was for twenty-four hours of abstinence from food. 

 The other was for a person who lost considerable weight as the result of excessive mus- 

 cular exertion. Even when no food is taken, a certain amount of heat must be produced, 

 and the standard animal temperature must be maintained. The heat thus produced can- 

 not be accounted for by the carbon discharged in carbonic acid, but it can be accounted 

 for by the hydrogen discharged in water, and it seems reasonably certain that water is 

 actually formed in the body. Under excessive exercise attended with loss of weight, it 

 seems certain that water is produced in the body by a union of hydrogen and oxygen. 

 Animal heat is undoubtedly produced very largely by oxidation; and it has been shown 

 that muscular work, while it has a tendency to raise the animal temperature, very con- 

 siderably increases the elimination of water. 1 The chemical products of this oxidation 

 are represented mainly by urea, as far as nitrogen is concerned, and by carbonic acid 

 and water. There are thus three elements with which the oxygen combines; viz., nitro- 

 gen, carbon, and hydrogen. We cannot account for the total amount of heat produced 

 in the body by the urea and carbonic acid discharged, but this can be accounted for by 

 supposing that a certain quantity of hydrogen is oxidized in the body to form water. 



We do not pretend to assert that the oxygen absorbed by the blood in its passage 

 through the lungs forms a direct and immediate union with carbon and hydrogen to form 

 carbonic acid and water. If such a union take place, carbonic acid and water are the 

 final products resulting from a series of /nolecular changes, the various steps of which we 

 are unable to follow ; but it is probably true that, if a union of oxygen with carbon and 

 hydrogen will produce a definite amount of heat, the quantity of heat is the same 

 whether the combination be slow or rapid. As regards the oxidation of carbon and hy- 

 drogen, -all that it is necessary to show is that carbonic acid and water are actually pro- 

 duced in the body, as a part of the final results of the intricate molecular changes involved 

 in nutrition and disassimilation. There is no good reason to suppose that the processes 

 of physiological wear or disassimilation are radically changed in their character during a 

 short period of abstinence from food, or during exercise which for a time wastes the tis- 

 sues more rapidly than they can be repaired. When the appropriation of nutritive mat- 

 ters produces an equilibrium between the physiological waste and repair, it is logical to 

 conclude that the waste of the tissues, which involves the oxidation of a certain quantity 

 of carbon, nitrogen, and possibly hydrogen, is repaired by the food, the nature of the 



1 Pettenkofer and Yoit, as one of the conclusions arrived at by experiments upon a man twenty-eight years of age, 

 kept for twenty-four hours in their large respiration-apparatus, make the following statement : " The elimination of 

 water is very much increased by work, and the increase continues during the ensuing hours of sleep." (Journal of 

 Anatomy and Physiology, Cambridge and London, 1868, vol. ii., p. 181.) 



