It is clear that the reserve of energy thus expended must be replaced, because the organism remains in equilibrium. Alimentation provides for this.
How does it provide for it? This is a question which deserves detailed examination. We cannot incidentally treat it in full; we can only indicate its main features.
How the supply of Reserve Stuff is kept up.—We know that food does not directly replace the reserve of energy consumed by the functional activity. It is not its potential chemical energy which replaces, purely and simply, the energy brought into play, consumed, or, better still, transformed in the active organ, or tissue. Food as it is introduced, inert food, does not, in fact, take up its place as it is, without undergoing changes in that organ and that tissue, in order to restore the status quo ante.
Before building up the tissue it will have undergone various modifications in the digestive apparatus. It will have also undergone changes in the circulatory apparatus, in the liver, and in the very organ we are considering. It is after all these changes that assimilation takes place. It will find its place and will have then passed into the state of reserve.
The food digested, modified, and finally incorporated as an integral part in the tissue in which it will be expended, is therefore in a new state, differing more or less from its state when it was ingested. It is a part of the living tissue in the state of constitutive reserve. Its potential chemical energy is not the same as that of the food introduced. It may differ from it very remarkably in consequence of sudden alterations.
We do not know for certain at the expense of what category of foods this or that given organ builds up its reserve stuff. There is a belief, for instance, according to M. Chauveau, that the muscle does its work at the expense of the reserve of glycogen which it contains. The potential chemical energy of this substance would be a source of muscular mechanical energy. But we do not know exactly at the expense of what foods, albumenoids, fats, or carbohydrates the muscle builds up the reserve of glycogen expended during its contraction. It is probable that it builds it up at the expense of each of the three categories after the various more or less simple alterations undergone by the materials in the digestive tube, the blood, the liver, or other organs.
This building up of reserve stuff, the complement and counterpart of functional destruction, is not chemical synthesis. It is, on the contrary, generally, and on the whole, a simplification of the food that has been introduced. This is true, at least as far as the muscle is concerned. However, to this operation, Claude Bernard has given the name of organizing synthesis, but the phrase is not a happy one. But in no case was the eminent physiologist deceived as to the character of the operation. “The organizing synthesis,” says he, “remains internal, silent, hidden in its phenomenal expression, gathering together noiselessly the materials which will be expended.”
These considerations enable us to understand the existence of the two great categories into which the eminent physiologist divides the phenomena of animal life: the phenomena of the destruction of reserve-stuff corresponding to functional facts—that is to say expenditures of energy; and the plastic phenomena of the building-up of reserves of organic regeneration, corresponding to functional repose—i.e., to the supply of food to the tissues.
Distinction between Active Protoplasm and Reserve-stuff.—If it is not exactly in these terms that Claude Bernard formulated this fruitful idea, it is at any rate in this way that it is to be interpreted. This can be done by giving it a little more precision. We apply more rigorously than that great physiologist the distinction drawn by himself between really active and living protoplasm and the reserve-stuff which it prepares. To the latter is restricted the destruction by the functional activity and the building up by repose.
The classification of Claude Bernard is strictly true for reserve-stuff. It is easy to criticize the wavering and, as it were, dimly groping expressions in which the celebrated physiologist has shrouded his ideas. The old adage will excuse him: Obscuritate rerum verba obscurantur. In the depths of his ignorance he had a flash of genius; perhaps he did not find the definitive and, as it were, clearly-cut formula defining what was in his mind. But, in this respect, he has left his successors an easy task.