386 PRINCIPLES OF ANIMAL NUTRITION. 
years 1888 and 1891 digestion experiments were made * in which 
the total nitrogen metabolism + and the carbon of the food and of 
the visible excreta were determined. The ration in every case 
consisted of hay and a mixture of six parts of oats with one of cut 
straw; the chemical composition of these feeds was quite similar 
in the several experiments, the greatest variation being in the last 
experiment (October 16-22, 1891). 
From the results of these experiments the metabolism of 
energy in the respiration experiments is computed in the following 
manner: 
First, the results of the several digestion experiments are com- 
bined in such a way as to give an average corresponding to the ration 
during the respiration experiment. E.g.,in Period 1 (loc. cit., p. 256) 
the ration consisted of 6 kgs. of oats, 1 kg. of straw, and 6 kgs. of 
hay. As no single digestion experiment was made on just this 
ration, the results of the first one are taken four times, those of the 
second three times, and those of the third once, and the sums divided 
by eight. These averages are taken as representing the digestibility 
and the urinary carbon and nitrogen during the respiration experi- 
ment. 
Second, from the average carbon and nitrogen of the urine as 
thus obtained its content of urea and hippuric acid is computed, 
and from these data, on the assumption of average composition for 
the metabolized proteids, the portion of the elements of the latter 
completely oxidized in the body, from which again the amount of 
oxygen required and of carbon dioxide produced is computed. 
Third, from the computed amount of crude fiber digested, 
assuming it to have the composition C,H,,O,; and that 100 grams 
yield 4.7 grams of methane, is computed the oxygen required for 
its oxidation and the carbon dioxide resulting. 
Fourth, after subtracting the amounts of oxygen and carbon 
dioxide, as above computed, corresponding to the proteids and 
crude fiber oxidized, from the totals found in the respiration experi- 
ment, the remainders are divided between fat and carbohydrates 
* Loc. cit., pp. 211-236. 
{ The nitrogen of the feces was determined in the air-dried material. 
Subsequent experience has shown that there is some loss of nitrogen in air- 
drying. 
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