DIGESTIBILITY OF ALFALFA. 180e 
The urine voided in these trials was analyzed in order to 
determine the balance of income and outgo of nitrogen and 
the energy of the urine. The heat of combustion was deter- 
mined by evaporating 10 cc. of urine on an S. & S. absorp- 
tion block weighing about .7 gram. The heat of combustion 
per gram of the block was ascertained by trial. The phos- 
phoric acid was determined gravimetrically from the residue 
left in the determination of the heat of combustion. Table 
LXXXV gives the analysis of the urine samples. 
The total weight of each of the several nutrients in each 
food material and in the feces was calculated from the total 
weight of food and feces and the composition of these 
materials as given in tables LX XXIII and LXXXIV. As 
stated above, the difference between the total nutrients in 
the food consumed and thetotal nutrients in the feces rep- 
resents the amounts that can be used by the body. We can- 
not assume the same for the difference of the total calories 
or energy of the food and feces because the oxidation or 
burning of the protein in the body does not yield the same 
amount of heat or energy as it doesin the bomb calorimeter. 
In the body, the protein is oxidized to urea and similar 
compounds, while in the bomb calorimeter, the oxidation 
goes further, and water, carbon dioxid, and free nitrogen 
are the final products. Hence this difference of energy in food 
and feces is too large to represent what is actually available 
to the body, so we subtract the total energy of the urine 
from this difference and call the result available energy. 
Another method used to determine the calories or energy 
lost to the body in the organic matter of the urine is to mul- 
tiply the number of grams of digestible protein by 1.25. 
This is the factor as worked out by Atwater and his associ- 
ates.* This was the method used to determine the per cent 
of energy available to the body from alfalfa alone. In di- 
gestion experiments Nos. 9 and 10, this method was used 
for determining the per cent of available energy of total food 
as well because in this trial the heat of combustion was not 
determined. 
In the trials where other foods were used with the alfal- 
fa hay, the results that were actually obtained are the di- 
* Conn. (Storr’s) Station Report, 1899, p. 100. 
