INVESTIGATIONS ON THE METABOLISM OF MILCH COWS. 815 



From the above data the metabolism of energy in the animal body 

 can be calculated. One gram of protein burned in a calorimeter pro- 

 duces 5.711 calories (mean of Berthelot and Stohmann's determina- 

 tions). Combustion in the animal body is less complete since nitrogen 

 is excreted largely in the form of urea, therefore less energy is pro- 

 duced. According to Rubner 1 gm. of dry matter of ash-free protein 

 of tissue burned in the body of a fasting animal yields 4.4 calories. 

 Provided the animal is amply nourished, substances containing more 

 carbon and having a higher fuel value than urea are excreted in the urine, 

 therefore the energy available from the combustion of protein is still less. 

 The true value in such cases can not be calculated with certainty, but 

 must be determined by accurate investigation in the individual experi- 

 ments. In most cases it is sufficiently accurate to assume that 1 gm. 

 of protein yields 4.1 calories when burned in the body. 



The heat of combustion of a gram of fat is 9.5 calories and of 1 gm. 

 of starch 4.18 calories. As noted above, the combustion of 100 gm. of 

 fat requires 288.75 gm. or 201.9 liters of oxygen. Each liter of oxygen 

 utilized for the combustion of fat produces 4.7 calories (950-^201.9=4.7) ; 

 100 gm. of starch requires for oxidation 118.5 gm. or 82.9 liters of oxy- 

 gen. Therefore each liter of oxygen used in the oxidation of starch 

 produces 5 calories (418-^-82.9=5). 



In the example cited above the total energy produced would be 1,046.6 

 calories, calculated as follows : 



100 v 17 Calories. 



t^L£L±i= 106.25 gm. protein Lurried in tbe body. 106.25x4.1 = 435.6 



The oxidation of fat requires 108.5 liters oxygen. 108.5 X 4.7 = 510.0 



The oxidation of starch requires 140.2 liters oxygen. 140.2 x5 = 701. 



Total „ 1,646.6 



In this computation no account is taken of the fact that in addition 

 to protein other nitrogenous materials, amids for instance, were con- 

 sumed, which also produce nitrogenous compounds in the urine but of 

 less fuel value than tbe compounds derived from protein. Further, 

 when large quantities of fat and starch are consumed fat will be 

 stored in the body. The amid nitrogen in the urine may be treated as 

 nitrogen derived from protein without serious error, since the assump- 

 tion is made that 46.6 gm. organic material in the urine is derived from 

 the cleavage of 100 gm. protein, and further since the fuel value of 

 protein is assumed to be 4.1 calories per gram. For very accurate 

 investigations, however, the above factors an not be used and actual 

 determinations of the values must be made. 



If the food is very abundant the formation of fat from starch is accom- 

 panied by cleavage of carbon dioxid from the starch molecule. Deducting 

 the values for the oxidation of protein the respiratory quotient in the 

 case becomes greater than 1. That is, the total quantity of oxygen 

 available for the oxidation of nitrogen free material should be assumed 



