I might quote a multitude of other palpable inconsistencies of the theory, which is so slippery that it can not be firmly grasped. Thus, Dr. Pavy (page 403), immediately after describing bacon-fat as "the most efficient kind of force-producing material," and stating that "the non-nitrogenous alimentary principles appear to possess a higher dietetic value than the nitrogenous," tells us that "the performance of work may be looked upon as necessitating a proportionate supply of nitrogenous alimentary matter," his reason for this admission being that such nitrogenous material is required for the nutrition of the muscles themselves.
A pretty tissue of inconsistencies is thus supplied! Non-nitrogenous food is the best force-producer—it corresponds to the fuel of the steam engine; the nitrogenous is necessary only to repair the machine. Nevertheless, when force-production is specially demanded, the food required is not the force-producer, but the special builder of muscles, the which muscles are not used up and renewed in doing the work.
It must be remembered that the whole of this modern theoretical fabric is built upon the experiments which are supposed to show that there is no more elimination of nitrogenous matter during hard work than during rest. Yet we are told that "the performance of work may be looked upon as necessitating a proportionate supply of nitrogenous alimentary matter," and that such material "is split up into two distinct portions, one containing the nitrogen, which is eliminated as useless." This thesis is proved by experiments showing (as asserted) that such elimination is not so proportioned.
In short, the modern theory presents us with the following pretty paradox: The consumption of nitrogenous food is proportionate to work done. The elimination of nitrogen is not proportionate to work done. The elimination of nitrogen is proportionate to the consumption of nitrogenous food.
I have tried hard to obtain a rational physiological view of the modern theory. When its advocates compare our food to the fuel of an engine, and maintain that its combustion directly supplies the moving power, what do they mean?
They can not suppose that the food is thus oxidized as food; yet such is implied. The work can not be done in the stomach, nor in the intestinal canal, nor in the mesenteric glands or their outlet, the thoracic duct. After leaving this, the food becomes organized living material, the blood being such. The question, therefore, as between the new theory and that of Liebig must be whether work is effected by the combustion of the blood itself, or the degradation of the working tissues, which are fed and renewed by the blood. Although this is so obviously the true physiological question, I have not found it thus stated.
Such being the case, the supposed analogy to the steam-engine breaks down altogether; in either case, the food is assimilated, is con-
