810 NUTRITION AND HEAT REGULATION. 



the body to digest and absorb protein food nitrogen equilibrium 

 may be maintained upon any given amount of protein. 



Carbon Equilibrium and Body Equilibrium. The term car- 

 bon equilibrium is sometimes used to describe the condition in which 

 the total carbon of the excreta (in the carbon dioxid, urea, etc.) is 

 balanced by the carbon of the food. It is possible that an individual 

 may be in nitrogen equilibrium and yet be losing or gaining in 

 weight, since, although the consumption of proteins may just be 

 covered by the proteins of the food, the comsumption of non-protein 

 material, particularly the fats of the body, may be greater than the 

 supply furnished by or manufactured from the food. An animal 

 may lose or gain in carbon when his nitrogen supply is in equilib- 

 rium. In the same way under special circumstances we may 

 speak of a water equilibrium or a salts equilibrium, although these 

 terms are not generally used. An adult under normal conditions 

 lives so as to maintain a general body equilibrium; his ingesta of 

 all kinds are balanced by the corresponding excretions, and the 

 individual maintains a practically constant body-weight. 



Complete Balance Experiments Respiration Chamber. 

 According to the statements made in the last paragraph, it is obvious 

 that if the analytical work is properly done, an exact balance may 

 be drawn between the proteins, fats, and carbohydrates eaten as 

 food and the proteins, fats, and carbohydrates destroyed in the 

 body as represented by the nitrogen and carbon contained in the 

 excreta. Complete experiments of this kind were attempted first 

 by Voit * and Pettenkofer, to whose work much of our fundamental 

 knowledge is due. In the experiments of these authors, made upon 

 men as well as animals, the total nitrogen of the urine and feces was 

 determined and the total quantity of CO 2 given off from the lungs 

 was estimated. This last determination was made possible by 

 placing the individual in a specially constructed chamber or respi- 

 ration apparatus. Air was drawn through this room by means of 

 a pump. The total quantity of air passing through the room was 

 measured by a gasometer and definite fractions were drawn off 

 from time to time for analysis of its CO 2 . From the figures thus 

 obtained it was possible to estimate the entire CO 2 given off during 

 the period of observation. Knowing the total nitrogen and carbon 

 eliminated, it is possible to estimate the amount of protein and 

 fat or carbohydrate destroyed in the body. If the carbon belong- 

 ing to the amount of protein metabolized is deducted from the total 

 carbon excreta, what is left represents either fat or carbohydrate 

 burnt in the body, and, knowing the amount of these materials 

 taken in the diet, it is possible to ascertain whether the correspond- 

 ing amount of carbon has all been excreted. By experiments of 

 * See Hermann's "Handbuch der Physiologic, " vol. vi., 1881. 



