150 - ORGANIC CONSTITUENTS OF ANIMAL FOOD. 
of matter constitutes the principal part of the fat of animals. — 
Of these oily and fatty matters, also, the chemical elements, — 
oxygen, hydrogen, and carbon, are the only ingredients ; but 
they are combined in proportions different from the last, the 
two latter predominating considerably. Hence they consti- 
tute another group of alimentary materials, to which the — 
term Oleaginous may be given.—Lastly, most Vegetables con- — 
tain, in greater or less amount, certain compounds which 
consist of the four elements, oxygen, hydrogen, carbon, and 
nitrogen, of which the animal tissues are composed. These — 
compounds exist most largely in the corn-grains, and also in 
the seeds of the pea and bean tribe; but there are few vege- — 
table substances used as food by animals, that do not contain 
them in some small amount. The gluten of wheat, the legu- — 
min of peas, and other vegetable substances of this kind, — 
together with the flesh of animals, the composition of which — 
(S 13) is identical with theirs, are united into a third group, 
to which the name Albuminous. is given.—We cannot pro- 
perly include in this group, however, the gelatinous portions 
of the animal tissues, which exist largely in gristle, bone, the — 
skin, and other parts ; because gelatin (the substance that 
forms glue), though it agrees with albumen in being made up 
of the four ingredients just named, differs from it extremely — 
in the proportions of those elements (§ 19); so that, although © 
there is good reason to believe that gelatin may be formed out 
of albumen, it does not seem that any albuminous compound ~ 
can be formed out of gelatin. Hence we must consider the — 
gelatinous compounds separately. { 
154. Of these four groups, the last two are distinguished as — 
azotized compounds, or substances that contain azote or nitro- i 
gen ; whilst the first two are spoken of as non-asotized, being — 
destitute of this element. The distinction is a very important 
one ; and must be kept steadily in view in considering the ulti- 
mate destination of each kind of food. It is obvious from what 
has been already stated as to the composition of the animal tis- 
sues ($$ 13—21), that azotized compounds must supply the chief ; 
materials for their nutrition and re-formation. The non-azotized — 
substances must be for the most part destined, unless converted 
into azotized compounds within the living body, either to be— 
simply deposited in its interstices, or to be thrown off from it 
again without ever actually forming part of its organised — 
structure. 
fe ie 
