
AVAILABILITY AND FUEL VALUE OF FOOD MATERIALS. 77 
contain more than 16 per cent. nitrogen.* It is probable that 
on the whole the factor 6.25 gives a tolerably accurate meas- 
urement of the protein of fish. The same is doubtless true of 
eggs. The protein of cow’s milk, according to the small num- 
ber of reliable investigations now available, appears to contain 
a trifle less than 16 per cent. of nitrogen, but hardly enough to 
warrant at present the use of any other factor than 6.25. It 
seems best, therefore, to retain this factor for the protein of all 
common animal food materials. 
The proteids of the cereal grains appear to contain on the 
average more than 16 per cent. of nitrogen. The proportion 
in different cereals has been the subject of study by a number. 
of investigators, notably Osbornet in this country and Ritt- 
hausen} in Hurope. Ritthausen in a review of this subject in 
1896 summarized the results of inquiry up to that time re- 
garding the proportions of nitrogen in different proteids. He 
grouped the cereals according to the average proportion of 
nitrogen in the total protein matter, making three classes, 
those containing approximately 17.5, 16.7 and 16 per cent. 
nitrogen respectively, or in other words, those in which the 
protein is computed by multiplying the nitrogen by the factor 
5.70, 6.00 and 6.25 respectively. WileyS has reviewed the 
work of Osborne upon the proteids of the different cereals and 
arrived at factors for the calculation of the protein in these 
products not materially different from those of Ritthausen. 
The grouping in Table 2 on page 79 conforms with the conclu- 
sions reached by these two investigators. 
We have found extremely few satisfactory data concerning 
_ the composition of the proteids of vegetables and fruits. In 
lack of more definite information concerning the exact propor- 
tion of nitrogen it seems best for the present to retain the cus- 
tomary factor, 6.25, for calculating the proteids, and, taking 
asparagin as the type of the non-proteids, to use the factor 4.7]| 
for estimating their amount. 
The factor for estimating the total nitrogenous matter or 
protein from the total nitrogen will thus depend upon the 

* In the flesh of the skate this may perhaps be due to the accumulation of urea or 
allied compounds in the tissues. 
+ Reports Conn. Agr. Exp. Sta., 1890, e7 seq. 
t Landw. Vers. Stat. 47 (1896), p. 391. 
2 U.S. Dept. Agr., Division of Chemistry, Bul. 13, Part IX., pp. 1171-1192. 
|| Asparagin contains 21.2 per cent. nitrogen. 
