CHEMICAL CHANGE AND HEAT PRODUCTION. 837 
The heat of combustion of fund may be determined in three ways — 
1 1 ) by direct estimation with a calorimeter, (2) by calculation from the 
oxygen necessary for oxidation, and (•">) by measurement of the heat 
produced by the combustion of the food inside the animal body. Such 
determinations have been made by Eubner, 1 and the following table is the 
isodynamic value of 100 grms. of fat estimated by these three modes: — 
First Method. 
Second Method. 
Third Method. 
100 grms. of Fat = 
l'roteid 
201 
193 
211 
Starch 
221 
240 
232 
Cane-sugar 
231 
249 
234 
Grape-sugar 
243 
263 
256 
It is to be noted that, with the exception of proteid, all food substances 
give too low a value for the heat of combustion when it is calculated from 
the equivalents of oxygen necessary for combustion. The calculation of the 
heat of combustion from the oxygen necessary for oxidation gives results 
which are not exact. 
The value of these calculations in the estimation of the heat pro- 
duced in a living body will be seen by comparing the results with those 
obtained by direct determination with the calorimeter. The following 
are Yierordt's 2 calculations for the heat production of an adult man in 
twenty-four hours : — 
(a) Calculation, according to Dulong's principle, from the heat of combus- 
tion of carbon and hydrogen. 
An adult man consumes in twenty-four hours — 
C. 
H. 
x. 
0. 
120 grms. proteid . 
64-18 
8-60 
18-88 
28-34 
90 „ fat 
70-20 
10-26 
9-54 
330 ,, carbohydrate 
146-82 
(Hydrogen 
combined wi 
th oxygen) 
281-20 
18-86 
18-88 
In urine and tieces 
29-80 
6-3 
... 
251-4 
12-56 
... 
... 
251-4 grms. C. x 8,080 
12-56 „ H. x 34,460 
Total heat production 
= 2,031,312 calories. 
= 432,818 
= 2,464,130 
1 Ztsehr.f. Biol., Miinchen, 1883, Bd. xix. S. 386. 
- "Grundriss der Physiol.," S. 281. 
