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AVAILABILITY AND FUEL VALUE OF FOOD MATERIALS. QI 
It has already been shown that the relative amount of non- 
proteids in the protein of vegetables and fruits is large. The 
potential energy of the protein of these foods is therefore rela- 
tively small owing to the low heat value of the non-proteids. 
Assuming 40 per cent. of the nitrogen in potatoes and other 
vegetables to exist in non-proteid compounds of which aspar- 
agin may be taken as the type, and 60 per cent. in proteids, 
with a heat of combustion of 5.8 calories per gram, the heat of 
combustion of one gram of vegetable protein or total nitrog- 
enous matter would be about 5.00 calories.* 
Since the nitrogenous matter of fruits appears to contain pro- 
portionately smaller amounts of the non-proteids than that of 
the vegetables, the heat of combustion of one gram of protein 
will be correspondingly greater. This heat of combustion may 
be computed upon the assumption that 30 per cent. of the 
nitrogen exists in non-proteid form of which asparagin may 
be taken as the type, and is approximately 5.20 calories 
per gram.y 
In the following table are given the average heats of com- 
bustion per gram of some of the proteids and non-proteids and 
the computed values for protein of different groups of food 
materials. 

* The details of the computations are as follows: 
1 g. N. = .6in proteids and .4 g. in non-proteids. 
Then 6 x 6.25 = 3.75 ¢. proteids x 5.80 = - - 21,8 calories, 
and .4x 4.70 = 1.88 g. non-proteids x 3.45 = - 6.5 calories, 
Ot: 5:03 Se Protein. = - - - 28.3 calories, 
and 1.00 g. protein = 5.03 calories. 
+ The details of the computations are as follows: 
ia 1 g. N. =.7g. in proteids and .3 in non-proteids. 
Then .7 x 6.25 = 4.38 g. proteids x 5.80 = - 2 25.4 calories, 
and .3x 4.70 = 1.41 g. non-proteids x 3.45 = - 4.9 calories, 
Ore R79 Ze protein: = - - - 30.3 calories, 
and 1.00 g. protein = 5.23 calories. 
