398 PRINCIPLES OF ANIMAL NUTRITION. 
by 45.20 grams. For the prevention of loss of tissue in this experi- 
ment, then, 250 parts of the dry matter of the meat were apparently 
equivalent to 100 parts of fat. The food, however, was given at the 
temperature of the room. To warm it and the 100 c.c. of water 
consumed to the temperature of the body would require an amount 
of heat equal to that produced by the oxidation of 1.4 grams of fat. 
Adding this to the 45.2 grams above gives 46.6 grams of fat as the 
equivalent of 113.38 grams of dry matter of the meat, or a ratio of 
100: 243. 
Another similar experiment gave as a final result a ratio of 
100: 253, or after correction for the warming of the food 100: 243, 
and a third longer experiment with extracted lean meat (syntonin) 
yielded the ratio 100: 227, or corrected as before 100: 225. 
If now, from the results of Rubner’s determinations of the met- 
abolizable energy of the proteids (p. 276), we compute the amount of 
each which contains the same quantity of metabolizable energy as 
100 grams of fat and compare it with the above ratios we have the 
following as the amounts equivalent to 100 grams of fat: 
Computed F A 
f Met- ‘ound in 
Dry Matter of— abolizable Eepeszacnts 
Gun’ _Grms. 
Lean meat: 
First experiment...... 235 243 
Second een eee 235 243 
Extracted meat......... 213 225 
The computed and observed equivalents differ by only 4.3 per 
cent. and 5.6 per cent. respectively, and hence Rubner concludes 
that protein replaces fat in metabolism substantially in inverse pro- 
portion to its “physiological heat value,” or, in other words, to its 
metabolizable energy. 
Rubner has also made similar experiments with cane-sugar and 
starch, comparing them in each case with the body fat, as in the 
above experiments, and has also made trials in which grape-sugar 
was substituted for the fat of the food. In computing the results 
of these experiments any change in the proteid metabolism was 
reduced to its equivalent in fat as computed from its metabolizable 
