5° PRINCIPLES OF ANIMAL NUTRITION. 
This conclusion, based on what appears to be the normal func- 
tion of the liver, is further strengthened by a large number of ex- 
periments and observations upon the metabolism in diabetes. 
This disease, whether arising spontaneously or provoked artificially, . 
is characterized by the presence of large amounts of sugar in the 
urine. It has been shown that this production of sugar continues 
when all carbohydrates are withdrawn from the diet, and further- 
more, that the amount of sugar excreted bears a quite constant. 
relation to the amount of proteids metabolized, thus clearly in- 
dicating the latter as the source of the sugar. It is true that the 
formation of sugar from proteids is denied by some physiologists,* 
but by the majority it seems to be accepted as a well-established 
fact that sugar is one of the intermediate products of proteid 
metabolism. 
Of the steps of the process, as well as of its quantitative rela- 
tions, we are ignorant. In effect, it is a process of oxidation and 
hydration, since a residue of the composition computed above 
would require the addition of both hydrogen and oxygen to con- 
vert it into sugar, but that it is as simple a process as this state- 
ment would make it appear, or that the conversion is a quantitative 
one, may well be doubted. 
In conclusion it may be stated that while recent investigations 
have shown the presence of a carbohydrate radicle in numerous 
(although by no means all) proteids, it does not appear that this 
fact stands in any direct relation to the physiological production of 
sugar from these substances. In the first place, the carbohydrate 
radicle constitutes a much smaller proportion of these proteids than 
corresponds to the amount of sugar which they are apparently 
capable of yielding in the body, and in the second place it appears 
to be a well-established (although not undisputed) fact that the 
organism can produce sugar from proteids which do not contain 
the carbohydrate radicle. 
Formation of Fat.—Whether fat is formed from the elements 
of proteids in the animal body is at present a subject of controversy, 
but this question will be more profitably considered in a subsequent 
chapter. It is sufficient to remark here that while much of the 
earlier evidence bearing upon this point has been shown to be 
*Cf. Schéndorf, Arch. ges. Physiol., 82, 60. 
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