Page:Popular Science Monthly Volume 24.djvu/398

384 =0·70. Other natural fats would give results differing little from this ratio.

The carbohydrates, on the other hand, contain relatively more oxygen than the other classes of foods, and contain hydrogen and oxygen in just such proportions as exist in water. Hence by their oxidation just enough oxygen must be consumed to convert the carbon to carbonic-acid gas, e. g.:

C6H10O6 $$+$$ 12O $$=$$ 6CO2 $$+$$ 5H2O.

C6H12O6 $$+$$ 12O $$=$$ 6CO2 $$+$$ 5H2O.

The ratio is hence 1 for all this class, since the carbonic acid formed is equal to the volume of the additional oxygen consumed. It follows, then, that the oxidation in the organism of carbohydrates would tend to cause the ratio $CO_{2}⁄O_{2}$ to approach unity. The extensive investigations of Regnault and Reiset on small animals have shown that with carbohydrate food the ratio does approach unity, sometimes almost attaining it, though of course it is impossible to eliminate entirely the decomposition of fats and albuminoids in the organism, and hence the ratio is kept below that figure.

So, also, as we have seen above, the tendency of muscular exertion is to increase this ratio and cause it to approach unity. The evidence, then, seems to point with tolerable conclusiveness to the fact that the immediate fuel-material is mainly non-nitrogenous and carbohydrate in its character. To what extent this supply of carbohydrates is derived from the glycogen of the muscles, to what extent from sugars absorbed from digestion, or produced from the glycogen of the liver, is not yet established with sufficient accuracy, though the participation of the muscle-glycogen is hard to doubt.

We have said the immediate fuel-material is apparently carbohydrates, for the possibility still remains that this carbohydrate material may itself be in part derived from albuminoids. It is certain that the liver-glycogen is in great part, possibly entirely, derived from albuminoids. Parke's experiments, above mentioned, showing a continuous elimination of increased quantities of nitrogen in the form of urea