100 STORRS AGRICULTURAL EXPERIMENT STATION. 
We measure the protein by multiplying the nitrogen by a 
given factor which varies with different food materials. The 
factor for computing the total protein of a given diet is decided 
by the proportions of the different food materials and their 
several nitrogen factors. We assume that the nitrogen factor 
is the same for the available protein as for the corresponding 
total protein. It may be that later inquiry will show that this 
assumption is incorrect, but in lack of more accurate knowledge 
we can do no better than follow the present plan. 
The heat of combustion of the water-free substance of the 
urine is determined by the usual method of oxidation by means 
of the bomb calorimeter and can be compared with the corre- 
sponding nitrogen of the urine, thus showing the ratio of 
nitrogen to the heat of combustion. <A similar ratio of nitro- 
gen to heat of combustion of protein could be established if 
necessary. 
A considerable amount of experimental data has accumulated 
in this laboratory within the past few years concerning this 
ratio of nitrogen to energy in the urine. A few like determi- 
nations* have been made by Prof. Chas. D. Woods, formerly of 
this Station and now Director of the Maine Experiment Sta- 
tion. As the average of forty-six determinations of this ratio 
it was found that for every gram of nitrogen in the urine 
there was unoxidized material sufficient -to yield 7.9 calories of 
energy. On the assumption already made that all the energy 
in the urine is derived from incompletely oxidized available 
protein, we may substitute for the ratio of nitrogen to energy 
the ratio of available protein to energy. ‘This value is found 
in the following manner: One gram of nitrogen in the urine is 
assumed to represent the breaking down or catabolism of 6.2 5 
grams of available protein of food or of body protein. ‘This 
assumption is slightly inaccurate owing to the presence in the 
food of some proteids, such as those of wheat and rye, and 
more especially the non-proteids containing more than 16 per 
cent. of nitrogen. It does, however, come close to the truth. 
For every 6.25 grams of protein consumed, therefore, there 
would be 7.9 calories of energy in the unoxidized materials 
of the urine, or about 1.25 calories per gram (7.9 blah 
126), 

* Unpublished. 


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