150 PRINCIPLES OF ANIMAL NUTRITION. 
siderable proportion of this meat was replaced by fat, starch, or 
sugar, not only was the nitrogen equilibrium maintained but the 
same was true of the carbon, as appears from the following averages 
computed from Atwater & Langworthy’s “Digest of Metabolism 
Experiments.” * The results of Pettenkofer & Voit’s first series 
with 1500 grams of lean meat as given by them are also included 
in the table: 
Gain or Loss 
Food per Day. by Body. 
Grape-|__ 
Meat, | Fat, | Starch, |sugar,|Nitrogen,| Carbon, 
Grms.|Grms.| Grms. | @rms.| Grms. Grms. 
Proteids only: 
Series: [cc lsslsg dace asa ee bane 1500) ... ange Peldace 0 + 3.3 
Average of all (22 experiments) | 1500] ... see | wee | $0.6] + 8.7 
Proteids and fat: 
100 grms. fat (1 experiment) ..| 500] 100 cee [ eee | $0.3 | 427.1 
200 “ — “ (5 experiments).| 500! 200 wee | ee. | —0.6 | 467.3 
Proteids and carbohydrates : 
Starch (8 experiments) ....... 500} 5.3 | 200; ... | —1.8; + 9.0 
Grape-sugar (3 experiments) ..| 500] ... ... | 200 | —1.3 | + 7.2 
While it is true, as was stated on page 109, that there is reason 
to suppose the carbon balance as computed by Pettenkofer & 
Voit to be somewhat in error, this in no way affects the general 
showing of the above averages. The introduction into the diet of 
100-200 grams of fat or carbohydrates made it possible to dispense 
with two thirds of the proteids previously required to maintain the 
animal, the remaining 500 grams of meat being nearly or quite suffi- 
cient to maintain nitrogen equilibrium. The fat or carbohydrates 
added were obviously used by the organism as sources of energy in 
place of the proteids (or their non-nitrogenous residue) oxidized 
for this purpose on a purely proteid diet, since the stored fat of the 
body was not only conserved but even shows a gain. 
Rubner’s investigations upon the source of animal heat ¢ afford 
*U. 8. Dept. Agr., Office of Expt. Stations, Bull. 45. Compare Zeit. f. 
Biol., 7, 450-480; 9, 6-13 and 450-467. 
+ Zeit. £. Biol., 30, 125-132, 
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