88 STORRS AGRICULTURAL EXPERIMENT STATION. 
close in these particular instances are due to an accidental bal- 
ancing of errors. We do not assume that the coefficients of 
Table 4 represent the actual availability of the nutrients of the 
different kinds of food materials under all circumstances or in 
all of the food materials of any given class. It does seem 
to us, however, that such comparisons as those in Table 5 
indicate that these coefficients represent a reasonably close 
approximation to the actual availability in the average mixed 
diet. 
HEATS OF COMBUSTION OF NUTRIENTS. 
The potential energy of any given substance is usually taken 
as equivalent to its heats of combustion determined by burn- 
ing a known weight of the substance in oxygen. ‘The actual 
amount of energy which the body can obtain from a given 
food material or diet depends upon various factors, the chief 
of which are the amounts and potential energy of the available 
nutrients of the food and the amount of incompletely oxidized 
material rejected in the urine. 
The heats of combustion of a very large number of indi- 
vidual food materials have been determined, but the data con- 
cerning the heats of combustion of definite chemical compounds 
occurring in the food of man are much more limited. It is to 
Stohmann, Berthelot, and their associates that we are indebted 
for by far the greater part of the data now available, although 
within a few years a considerable number of determinations 
have been made in this country, mostly in connection with 
the nutrition investigations carried on under the auspices of 
the U. S. Department of Agriculture.* 
HEATS OF COMBUSTION OF PROTEIDS, NON-PROTEIDS, AND 
PROTEIN OF FOOD MATERIALS. 
The heat of combustion of different proteids varies within 
certain limits, but is in all cases much larger than that of the 

* See summaries of results of these inquiries as given by Stohmann, U.S. Dept. 
, Agr., Experiment Station Record, Vol. VI., Pp. 590; by Berthelot in Thermochimie, 
Vol. IL, and by Atwater in Bulletin No. 21, U.S. Dept. Agr., Office of Experiment 
Stations. 
It is expected that details of a compilation of the heats of combustion of different 
compounds and groups of compounds occurring in food materials will be published 
in the near future in a Bulletin of the Office of Experiment Stations, 


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