




AVAILABILITY AND FUEL VALUE OF FOOD MATERIALS. Hibs 
capable of being transformed into nitrogenous body tissue, and 
thus go to form the blood, muscle, tendon, brain, nerves, etc. 
The non-proteids appear to have but little nutritive value, 
unless it be in some cases, for fuel. It may be that some of 
them have an especial value as sparers of protein, z. ¢., for 
protecting the protein of food or body tissue from consump- 
tion. But too little is known of their functions to warrant 
very definite assumptions.* 
Proportion of proteids and non-protetds.—In analyses of food 
materials by current methods it is the almost universal practice 
to take the product obtained by multiplying the total nitrogen 
of the food by 6.25 asa measure of the total nitrogenous mate- 
tial, z. €., protein; in other words, to assume that protein con- 
tains 16 per cent. nitrogen. This involves two errors. In 
the first place the proportion of nitrogen in the non-proteids 
taken collectively is greater than in the proteids, and multi- 
plying the nitrogen by 6.25 gives a value generally greater 
than the actual amount of nitrogenous material. In the sec- 
ond place the non-proteids have little nutritive value. ~ Both 
these errors, therefore, tend to make the estimate of nutritive 
value too large. It would perhaps be better to leave the non- 
proteids out of account in estimating the nitrogenous, 7. e., 
tissue-forming material of food. Unfortunately our present 
chemical methods for the separation of the proteids and non- 
-proteids in food materials are unsatisfactory. The compara- 
tively few determinations now on record of the proportions in 
a given food material do not accord with each other and cannot 
be considered reliable. Until exact information concerning the 
- proportion of proteids and non-proteids in different classes of 
food materials is obtained recourse must be had to the best 
data available. In flesh the proportion of non-proteids, z. @., 
so-called extractives or meat bases, appears to be larger than 
has sometimes been supposed, but the data upon the subject 
are very inadequate. 
The nitrogen in the cereal grains and their manufactured 
products is, like that of meats, mostly in the form of proteids, 
although a small proportion éxists in the form of amids, of 
* It has been suggested that asparagin may serve as nitrogenous nutriment for the 
- intestinal bacteria and thus protect the proteids which might otherwise be broken 
down. 
