
108 STORRS AGRICULTURAL EXPERIMENT STATION. 
In the estimates upon which these figures are based _Rubner 
made use of the heats of combustion of the compounds of the 
different classes of nutrients in so far as they were available at 
the time. For the potential energy of the material excreted 
in the urine he used the results of determinations of the nitro- 
gen and heats of combustion of the water-free substance of 
the urine of dogs with a diet of meat. He assumed that 60 
per cent. of the protein of ordinary mixed diet was of animal 
and 40 per cent. of vegetable origin. He made allowance for. 
the energy in the feces as determined by experiments with 
dogs on a meat diet, but made no allowance for any undi- 
gested residue of the fats and carbohydrates of the food. ‘To 
state the case in another way, he assumed the fuel value 
(‘‘Warmewerth’’) of the fats and carbohydrates to be the 
same as their heats of combustion, but estimated the similar 
factors for the protein by subtracting the heat of combustion of 
feces and urine from the total heat of combustion of the protein 
of the food. Considering the paucity of his data and the fact 
that he made no allowance for either the undigested material 
or the metabolic products of the feces properly belonging to 
the carbohydrates and fats, the results are certainly very close 
to those to which we are led by the use of the more extensive. 
data now available. The closeness of this agreement appears 
to be partially due toa balancing of errors. ‘The heats of com- 
bustion which Rubner used were largely those determined by 
means of the Thompson-Stohmann calorimeter, which gave 
rather too low results. We hope to discuss this subject more 
fully in a later article. 
SUMMARY. 
Lhe object of the preceding discussion is to deduce factors for 
estimating the nutritive values of materials used Sor the food of 
man. | ) 
Lhe principal data used for these estimations are the percent- 
ages, coefficients of availability, heats of combustion, and fuel 
values of the protein, fats, and carbohydrates in food materials 
and the proportional amounts of different kinds of foods used in 
the average diet. The proportions of nutrients in ordinary food 
are found by analysis, There are now avatlable analyses of not 

