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 

 ( 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/<mr 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. 



1 54. Of these four groups, the last two are distinguished as 

 azotized compounds, or substances that contain azote or nitro- 

 gen ; whilst the first two are spoken of as non-azotized, being 

 destitute of this element. The distinction is a very important 

 one j 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 ( 1 3 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. 



