THE METABOLIC REQUIREMENTS OF THE BODY 1055 



unless the animal has been nourished exclusively on protein material 

 and is not in possession of normal amounts of glycogen and fat. Thus, 

 Voit has found that an animal which is in fat and carbohydrate equi- 

 librium does not exhibit a nitrogenous breakdown, and concluded, there- 

 fore, that the extra energy is derived wholly from the non-nitrogenous 

 constituents of the body. 



These results soon found support in the experiments of Fick and 

 Wislecinus, who ascended the Faulhorn to a height of 1956 meters. 

 By comparing their weight with the height to which they climbed, it 

 was possible to compute the amount of work performed by each of 

 them. In the case of Fick, it amounted to 66 X 1956 = 129,096 

 kilogrammeters plus about 30,000 kilogrammeters of work performed 

 by the heart and muscles of respiration. Since only non-nitrogenous 

 food had been ingested by these investigators during a period of 17 

 hours before thie climb as well as during it, the urea eliminated by 

 them must have been derived entirely from their body-proteins. On 

 determining the heat value of this urea, it was found to be entirely 

 insufficient to account for the amount of work done. Very similar 

 results have been obtained by Parkes upon soldiers during periods of 

 rest and long marches, and by Atwater by means of the respiration 

 calorimeter. 



It may be concluded, therefore, that ordinary muscular work does 

 not increase the metabolism of the proteins much beyond its normal 

 value, provided sufficient non-nitrogenous material is at hand to pro- 

 duce the required amount of extra energy. Accordingly, if the non- 

 nitrogenous substances are present in insufficient quantity, some of 

 this extra energy must be derived from the proteins. The elimination 

 of nitrogen in the urine is then increased, and naturally, this waste 

 must be the greater the more intense the muscular exercise. 



Normal Metabolism. — The preceding discussion pertaining to 

 starvation is of special value, because it furnishes a means of deter- 

 mining the amounts of energy liberated by the body under normal 

 conditions, and allows us to ascertain the amount of fuel which must 

 be ingested in order to supply this energy. It will be found that a 

 marked difference exists between the various foodstuffs in this regard. 

 In the first place, it should be noted that an animal fed on pure fat 

 or carbohydrate, or a mixture of the two, does not survive thi« diet 

 for a much longer period than if all food were withheld. Consequently, 

 this diet is only little better than actual starvation. On a diet of 

 proteins, salts and water, on the other hand, the animal most generally 

 survives. In the second place, it is not correct to assume that an 

 animal may be kept in equilibrium for any particular foodstuff if 

 the intake is exactly balanced with the waste. 



This is true in particular of the proteins. Thus, if a starving 

 animal is fed an amount of protein which exactly balances the output 

 of nitrogen, the excretion of the latter rises to a level practically equal 

 to that of starvation, plus that of the protein ingested. This implies 



