METABOLISM. 49 
typical metabolic product, and using average figures for the com- 
position of animal proteids, we have, omitting the sulphur of the 
proteids, the following: 
Proteids. Urea. Residue. 
Carbon.............. 53.0 6.86 46.14 
Hydrogen ............ 7.0 2.29 4.71 
Oxygen ........ .... 24,0 9.14 14.86 
Nitrogen ............ 16.0 16.00 
100.0 34.29 65.71 
After abstracting the elements of urea, we have left considerably 
‘over half the hydrogen and oxygen of the proteid and the larger 
part of its carbon. A substantially similar result is reached in case 
of the other nitrogenous metabolic products. The splitting off of 
these products from the proteids leaves a non-nitrogenous residue. 
FatrE oF THE Non-niTRoGENoUsS ReEsipuE.—The foregoing 
statements and comparison must not be understood to mean that 
the proteids split up in the body into two parts, viz., urea, etc., on 
the one hand, and an unknown non-nitrogenous substance or sub- 
stances on the other. As we have already seen, the processes of 
proteid metabolism are far more complicated than such a simple 
cleavage. Neither are we to assume that any substance or group 
of substances corresponding in composition to the “residue” of the 
above .computation exists. The figures mean simply that while 
the nitrogenous bodies of the urine contain all the nitrogen of the 
proteids they do not account for all of the other elements, but that 
part of the latter must be sought elsewhere. 
Ultimately, of course, the elements of this non-nitrogenous 
residue are converted into carbon dioxide and water. The conver- 
sion into these final products, however, is necessarily a process of 
oxidation, presumably yielding energy to the organism. It is a 
matter of some interest, then, to trace the steps of the transforma- 
tion so far as this is at present possible. 
Formation of Sugar.—In discussing the functions of the liver in 
8 1 of this chapter, we have seen reason to believe that this organ 
continues to produce sugar when the diet consists largely or exclu- 
sively of proteids. In this case we are forced to the conclusion that 
this sugar is manufactured from the elements of the non-nitrogenous 
residue. 
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