756 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
Ill other words, the insoluble protein was not directly determined, 
but was estimated by difference. 
Since this is one of the most important constituents of the flesh, 
Alin^n had recourse to direct determination of nitrogen and the com- 
putation of the amount of total protein matters from the percentage 
thus obtained. 
PERCENTAGE OF NITROGEN IN PROTEIN COMPOUNDS. 
The subject of the percentages of nitrogen in the flesh of fish is treated 
at some length by Almen. I quote his language : 
The percentage of' nitrogen, without doubt, demands special consideration, because 
it is a measure of the amount of protein compounds. When we consider the vary- 
ing percentage of fat, we might expect wide variations. The amounts of nitrogen 
in the flesh of fish, however, range between 2.1 per cent, and 3.2 per cent., while beef 
contains3.33percent. The plaice comes next to beef, with 3.20 per cent. Consequently 
it contains more protein matters than any other fish studied. By comparing the 
series (d) and (e) (of table 15 above) it will be seen that the percentages of nitro- 
gen are a correct measure of the relative amounts of protein. 
The amount of protein computed from the determined percentages of nitrogen 
depends, of course, upon the number by which the latter percentages are multiplied 
or, in other words* upon the nitrogen percentage-coefficient [nitrogen factor] of the 
flesh. The percentage of nitrogen in the true protein compounds [albuminoids and 
gelatinoids] varies from 15.4 to 16.5 percent., and averages 16 per cent., from which 
it follows that/to obtain the percentage of actual protein compounds, we have to 
multiply the nitrogen in the latter by 6.25, or, in other words, 6.25 is the nitrogen 
percentage-coefficient (nitrogen factor) for pure protein compounds in general. This 
coefficient is often used in calculating the amount of protein in vegetable as well as 
in animal food materials. 
Referring now to the amount of protein compounds in the flesh of fish, it may be 
noted that Payen gives the nitrogen percentages of different fish aud adds (in a foot- 
note) that the amount of protein may be obtained by multiplying the percentage of 
nitrogen by 6.5. Letheby, in like manner, in a table of the composition of various 
food materials, gives their contents of nitrogen and protein compounds, the latter 
being 6.5 times as large as the former. Pavy employs the same coefficient, following 
the figures in Letheby’s table. 
This method of calculating the amount of protein compounds in meat and other food 
materials in the same way as for pure protein compounds, namely, by multiplying 
the nitrogen percentages by 6.25, leads to gross errors, because flesh is in no way pure 
protein, but contains a number of other ingredients, namely the extractive matters, 
some of which are non-nitrogenous (inosite), while others which are rich in nitrogen 
(kreatin, hypoxanthin, etc.) might, with as good reason, be counted as worthless as 
ranked with protein. The common “ Liebig's meat extract ” is said to contain 9 to 
10 per cent, of nitrogen and 33 to 40 per cent, of salts and water. Taking these out, 
the remainder corresponds to the water-free extractive matters, which are said to 
contain about 15 per cent, of nitrogen or nearly the same proportion as the pure pro- 
tein compounds. Now, since flesh contains about 2 per cent, of extractive matters 
with about the same content of nitrogen as the protein compounds, it is clear that the 
amount of protein compounds obtained by multiplying the nitrogen by 6.25 must be 
too large, and in no way corresponds to the actual quantity of pure protein compounds 
present but, rather, very closely to the sum of these and the extractive matters. 
Alm^n’s point, that multiplying the total nitrogen, including that 
which belongs to the extractives as well as that in the protein com- 
pounds, albuminoids, and gelatinoids, by 6.25 would give a product 
