METHODS OF INVESTIGATION. 75 
compounds in the urine. Chauveau & Kaufmann,* starting with 
an empirical formula for albumin, represent its complete meta- 
bolism in the body by the equation 
2WCpH rN 1g0nS + 1510, = 18CH,N,O + 126CO, + 76H,0 +S,, 
thus obtaining the respiratory quotient in =0.8344, neglecting 
the oxygen required to oxidize the sulphur. 
The urine, however, always contains greater or less quantities 
of nitrogenous compounds richer in carbon than urea, and in herbiv- 
orous animals in particular such compounds are abundant. The 
respiratory quotient of the proteids is therefore variable, depend- 
ing upon the extent to which their carbon is completely oxidized. 
Thus Zuntz and Hagemann f{ in an experiment upon the horse 
in which approximately 15 per cent. of the total nitrogen of the 
urine was contained in hippuric acid, compute it at 0.765. 
Deductions from Respiratory Quotient.—The value of a determi- 
nation of the respiratory quotient lies in the clue which it affords to 
the nature of the substances which are being oxidized in the body. 
Assuming that the materials available for oxidation in the schematic 
body are substantially proteids, carbohydrates and fat. it is evi- 
dent that when the quotient approaches 1.0 the material consumed 
must consist largely of carbohydrates, while if it falls to the neigh- 
borhood of 0.7 it is clear that the oxygen is combining chiefly with 
fat. An intermediate value, on the other hand, would be more am-: 
biguous, since it might result from the oxidation of proteids, carbo- 
hydrates and fat in several proportions. 
If, however, the amounts of oxygen consumed and of carbon 
dioxide produced in the oxidation of any one of the three groups be 
known, it is a simple matter to compute the proportion in which 
the other two enter into the reaction. For the amount of proteids 
metabolized, we have an approximate measure in the total urinary 
nitrogen. If we can also determine the amounts of carbon, hydro- 
gen and oxygen contained in these nitrogenous urinary products, 
we can compute the quantity of oxygen required to oxidize the non- 
nitrogenous residue of the proteids and the amount of carbon diox- 
ide resulting from it upon the assumption of complete oxidation. 
* Compare p. 51. ¢ Landw. Jahrb., 27, Supp. ITI, 240. 
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