the body during rest, and its connection with the laying up of a reserve of force: the oxygen enters into the supposed complex compound much as the nitric-acid radicle enters into nitro-glycerine or gun-cotton—it is held in a state of unstable equilibrium, ready to enter into new and simpler relations with its neighboring atoms, and to set free the force by which it was placed in its unstable position. The hypothesis explains also that necessity for albuminoids in the food of the laboring animal which practical experience has shown to exist, as well as the fact that there is no greater excretion of nitrogen during work than during rest; the proteine serves as the basis for the alternate synthesis and analysis which constitute what might be called the atomic mechanism of muscular activity without itself being destroyed. Furthermore, it shows why we need rest after work; in the first place, the circulation must have an opportunity to remove those waste products which accumulate in the working muscle faster than they can be carried off, and in the second place a fresh supply of force must be stored up in the way described before it is ready to be used at the command of the will.
Thus this theory explains all the facts now known, and, while it is but an hypothesis, it is still based on the "scientific use of the imagination," and indicates the direction in which we may confidently look for an advance of positive knowledge.
If it be true, much of the current discussion upon the source of muscular power is but a "strife of tongues"; both proteine and nonnitrogenous substance are necessary, and an inquiry as to which is the source of the power would resemble an inquiry as to whether the explosive force of nitro-glycerine was derived from the glycerine or the nitric acid used in its manufacture, and would be a question of metaphysics rather than of natural science.
It might be asked, since this is a question of transformation of energy, why we do not apply the law of the conservation of energy, and from the heat of combustion of the various elements of food calculate their value as reservoirs of force by Joule's formula. This has been frequently attempted, notably by Fick and Wislicenus in their experiments already alluded to. These investigators showed that the amount of force contained in the proteine which was destroyed in their bodies during the ascent of the Faulhorn was insufficient, if wholly converted into motion, to raise their bodies to the height of the mountain.
Various other attempts at the same sort of calculation have been made, with more or less of care and insight: we may mention here those of Dr. Pavy, which rest on several assumptions of questionable accuracy; and those of Professor Flint, made upon the same plan, with the object of showing the worthlessness of Dr. Pavy's—an object which he has doubtless attained.
It would carry us too far to discuss here the value of these results,
