4 CHEMICAL BASIS OF THE ANIMAL BODY 



some representatives of carbohydrates and fats as well as of pro- 

 teids. We might perhaps even go as far as to say that, in all 

 forms of living substance, the proteid basis is found upon analysis 

 to have some carbohydrate and some kind of fat associated with 

 it. Further, not only does the normal food which is eventually 

 built up into living substance consist of all three classes, but, as 

 we have seen in the sections on nutrition, gives rise by meta- 

 bolism to members of the same three classes ; and as far as we 

 know at present, carbohydrates and fats, when formed in the 

 body out of proteid food, are so formed by the agency of living 

 substance, by the action of some living tissue. Hence there is at 

 least some reason for thinking it probable that the molecule of 

 living substance, if we may use such a phrase, is far more com- 

 plex than a molecule of proteid matter, that it contains in itself 

 residues so to speak not only of proteid,, but also of carbohydrate 

 and fatty material. 



The plasmodium of ^tlialiurn septicurn, a myxomyeaetous fungus, 

 presents a convenient source of extremely primitive protoplasm which 

 maj* be obtained in large quantities. It occurs as an extended, yel- 

 low, gelatinous mass, frequently of considerable thickness, on the 

 surface of heaps of spent tan or other similar decaying vegetable 

 matter, and exhibits very active movements both internally and more 

 particularly at its edges, of an essentially amoeboid nature. It has 

 been .carefully analysed by Reinke, Studien uber das Protoplasma, 

 Berlin, 1881. See also Krukenberg, Unters. a. d. physiol. Inst. 

 Heidelb., Bd. n. 1882, S. 273. 



Whether this be so or not, for at present no dogmatic state- 

 ment can be made, there is no doubt that when we examine the 

 various tissues and fluids of the animal body from a chemical 

 point of view we find present in different places, or at different 

 times in the same tissue or fluid, several varieties and derivatives 

 of the three chief classes ; we find many forms of proteids, and 

 bodies closely allied to proteids, in the forms of mucin, gelatine, 

 &c. ; many varieties of fats ; and several kinds of carbohydrates. 



We find, moreover, many other substances which we may re- 

 gard as stages in the constructive or destructive metabolism of 

 the various forms and phases of living matter, and which are im- 

 portant not so much from the quantity in which they occur in the 

 animal body at any one time as from their throwing light on the 

 nature of animal metabolism ; these are such substances as urea, 

 uric acid, other organic crystalline bodies, and the extractives in 

 general. 



In the following pages the chemical features of the more 

 important of these various substances which are known to occur 

 in the animal body will be briefly considered, such characters 

 only being described as possess or promise to possess physio- 



