98 STORRS AGRICULTURAL EXPERIMENT STATION. 
There were at times quite marked variations between the heats 
of combustion actually found and those calculated, amounting 
in some cases to as much as 5 or even 6 per cent. of the former 
value. On the whole, however, the agreement is as close as 
could well be expected when we consider the relatively small 
amount of data upon which some of the assumptions involved 
in deriving the factors are based, and when we consider, on the 
other hand, the possibility of errors in the chemical analyses. 
Indeed, it seems to us that the agreement in a large number of 
cases has been sufficiently close to warrant the use of these 
factors as a check on the analytical work or on the determina- 
tions of the actual heats of combustion by means of the bomb 
calorimeter. Thus if marked discrepancies occur in any given 
case between the calculated heats of combustion and those de- 
termined by the bomb calorimeter, either the analytical work 
may well be repeated or the heat of combustion redetermined 
or both. Of course in some prepared foods made up of several 
different kinds of food materials, pastries for example, which 
contain an unknown proportion of sugars and starches, the 
calculated heat of combustion may differ considerably from 
the computed, and cannot be Hath as giving any check upon 
the analytical results. 
FUEL VALUE. 
In accordance with the definitions in the previous article 
(see pages 69-72) the fuel value of a given food material is 
measured by the difference between its heat of combustion and 
the heats of combustion of the corresponding feces and urine. 
It is assumed that under normal conditions the fats and carbo- 
hydrates are completely oxidized in the body, and that hence 
their fuel values will be their total heats of combustion less 
those of the unavailable portions; in.other words, the heats of 
combustion of the available portions. It is also assumed that 
all of the energy yielding material of the urine comes from the 
incomplete oxidation of the protein of the food. ‘The heat of 
combustion of protein as determined with the bomb calorimeter 
measures the heat evolved in the complete oxidation of the carbon 
to carbon dioxide, and the hydrogen to water, while the nitrogen 
remains in the free state. In the body, however, oxidation 
of nitrogenous compounds cannot be carried as far ane the 

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