832 METABOLISM. 



combustion yields 563.09 calories, and if we subtract the calorific value of the 

 corresponding urine ( = 113.70 calories) and feces ( = 17.76 calories), the sum, 

 131.46 calories, then 431.63 calories were set free in the body. For every gram 



of nitrogen eliminated in the urine (16.28 gram.) there is produced -r^-~r =26.51 



96.63 

 calories; the corresponding quantity of oxygen is ^"7^ = 5.91 liter Q an d the 



77 39 

 corresponding quanity of CO 2 produced is i^"oc = 4.75 liters CO 2 . The calorific 



value for 1 liter of oxygen consumed is therefore - ' =4.485 calories, and for 



o.y i 



1 liter of carbon dioxide produced ~r^- =5.579 calories. 



For milk protein ZUNTZ has calculated for 1 gram urea nitrogen 5.8 liters 

 oxygen, 4.6 liters carbon dioxide and 27 calories. The calorific value can be cal- 

 culated from this for 1 liter O = 4.66 and for 1 liter CO 2 = 5.87 calories. If we 

 take the average of these calculations we obtain a calorific value for the com- 

 bustion of protein, which for 1 liter of oxygen amounts to 4.573 calories and for 

 the carbon dioxide 5.725 calories. 



According to these calculations the combustion of proteins in the 

 animal body has a calorific value for 1 liter of oxygen of, in round numbers, 

 4.57 calories, and for 1 liter CO 2 , 5.73 calories. We therefore have the 

 following calorific values for the three foodstuffs: 



Per 1 liter Relative Per 1 liter Relative 



Oxygen. value. Carbon dioxide. value. 



Protein 4.57 100 5.73 113.4 



Fat 4.69 102.6 6.63 131.3 



Carbohydrate 5.05 110.5 5.05 100.0 



The figures for the oxygen vary less than those for the carbon dioxide, 

 and this is a reason why the oxygen values are better suited than the 

 CO 2 values for calculating the energy production from the extent of gas 

 exchange. Other investigators have obtained results which correspond 

 more or less with the above values for the heat value of oxygen, and E. 

 VOIT and KUMMACHER,* who have made calculations in another way, 

 have obtained still smaller differences for the relative oxygen value. 



From what was said above we can calculate the extent of protein 

 metabolism, the corresponding development of energy and the correspond- 

 ing absorption of oxygen and carbon dioxide formation from the quantity 

 of nitrogen in the urine. If we subtract the oxygen and carbon dioxide 

 values from the total, directly determined gas exchange, the result repre- 

 sents the fats and carbohydrates used. According to ZUNTZ from this 

 residue we can calculate the heat value of the oxygen used as well as the 

 division of the decomposition of the fat and carbohydrate by considering 

 the respiratory quotient. For this purpose ZUNTZ and SCHUMBURG have 



1 Voit, Zeitschr. f. Biol., 44; Kummacher, ibid. 



