84 PRINCIPLES OF ANIMAL NUTRITION. 
proteids in the food is exhausted, the proteid metabolism reaches 
a minimum and thereafter remains nearly constant for a consider- 
able time, and subsequent investigations have shown that this 
constancy is still more marked when the proteid metabolism is 
computed per unit of live weight. 
What has thus been found to be true of the proteid metabolism 
has also been shown to hold good of the total metabolism of pro- 
teids plus body fat. As soon as the influence of the previous food 
has disappeared, the rate of metabolism of both proteids and fat 
shows but slight variations throughout a considerable time. Of 
the early experiments of Pettenkofer and Voit, the following * may 
be cited as illustrating approximately this constancy: 
Series a, 1862. Series b, 1861. 
March 10, | March 14, Aptil 5, April 8, | April 11, 
6th Day. | 10th Day.|| 2d Day. | 5th Day. | 8th Day. 
: 2 Kgs. Kgs. Kgs. Kgs. Kgs. 
Live weight .........0.00 31-31 | 30.05 || 32-87] 31.67 | 30.54 
Grms, Grms. Grms. Grms. Grms. 
Carbon of excreta ........ 104.1 82.4 108.7 100.0 93.2 
Nitrogen of excreta....... 5.95 5.23 11.6 5.7 4.7 
Total loss: 
Proteids ............... 37.18 32.69 72.51 35.63 29 .38 
Bat cece Sbotuslasa leew avast 107. 83... 86. 103. 99.2 
Loss per Kg. live weight: 
Proteids ............... 1.19 1.09 2.21 1.13 0.96 
TOA sacs os ee oS “tus Raion 3.43 2.76 2.62 3.25 3.25 
Finkeler | determined the respiratory exchange of fasting 
guinea-pigs in two-hour periods. Upon the highly probable assump- 
tion that their proteid metabolism was relatively small and con- 
stant, the results of such experiments would furnish a measure of 
the relative intensity of the total metabolism. Finkeler’s average 
results are contained in the table on the opposite page. 
But a slight decrease in the amount of oxygen consumed is 
observed in the different stages of the fasting, while there is a 
marked decrease in the amount of carbon dioxide produced. The 
relation between these two quantities, as expressed by the respira- 
tory quotient,t shows us that at the beginning of the fasting’ the 
metabolism was largely at the expense of the carbohydrates of the 
* Zeit. f. Biol., 5, 369. Arch. ges. Physiol., 28,175. + Compare p. 74. 
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