§ 1 Effect of the Vital Activity. Destruction or Growth?
Distinction between the Living Substance and the Reserve-stuff mingled with it.—The physiology of nutrition has given rise to a vast body of research during the last half-century. Physiological schools, masters and pupils, such as the school at Munich under Voit and Pettenkofer, Pflüger’s at Bonn, Rubner’s, and those of Zuntz and von Noorden at Berlin, and a large number of zootechnical and agricultural laboratories through the whole world have for years past been engaged in analyzing ingesta and egesta, in drawing up schedules of nutrition, in order to determine the course of decomposition and reconstitution of the living material.
If I were asked what, in my opinion, is the most general result of all this labour, I would reply that it has affirmed and corroborated the important distinction which must be drawn between living substance, properly so called, and reserve-stuff. The latter, the reserve-stuff of albuminoids, carbohydrates, and fats, are so intimately intermingled with the living substance that they are in most cases very difficult to distinguish from it.
Organic Destruction.—A second point, which is placed equally beyond doubt, is that the vital functional activity is accompanied by a destruction of the immediate principles of the organism, in the direction of their simplification. This functional destruction cannot be doubted in the case of differentiated organs in which the functional activity is evident, intermittent, and in some measure distinct from the other vital phenomena which take place in them. For example, in the case of contracting muscles the respiratory carbonic acid and urinary carbon are the irrefutable proofs of this destruction: weak in repose, abundant during activity, and in proportion to it. There can be no doubt on this point. The truth laid down by Claude Bernard under the name of the law of functional destruction has been doubly consecrated by experiment and theory. According to the energetic theory, in fact, mechanical and thermal energies manifested in the vital functional activity can only have their source in the chemical energy set free by the destruction of the immediate principles of the organism, reduced to a lower degree of complexity.
Destruction of Reserve-stuff.—But now the disagreement begins. What are these decomposed, destroyed principles? Do they belong to the cellular reserve-stuff or to the living matter properly so called? There is no doubt that most of them belong to the reserve-stuff. For example, this is especially true of glycogen, which is consumed in muscular contraction just as coal is consumed in the furnace of the locomotive; and glycogen is a reserve-stuff of muscle. These reserve-stuffs destroyed in the functional activity can be built up again only during repose.
But it is not yet certain whether the living matter itself, the active protoplasm, the muscular protoplasm, takes part in this destruction, whether it provides it with elements. Experiments have proved contradictory. Experimenters have isolated the nitrogenous wastes (urea) after muscular labour, and they have compared them with the wastes of the period of repose. These nitrogenous wastes bear witness to the destruction of albuminoid substances, and the latter are the constituent principles of living matter. If—under conditions of sufficient alimentation—the muscular functional activity involves more nitrogenous waste, i.e., a greater destruction of albuminoids, it might be supposed that the living material properly so called has been used up and destroyed for its own purposes. (And here again there might be a reserve-stuff of albuminoids, distinct from the living protoplasm itself, and more or less incorporated with it.)
But experiment so far has not given decisive results. The latest experimental researches, such as those of Igo Kaup, of Vienna, which date from 1902, tell us as uncertain a tale as their predecessors. The increase in the destruction of albumen has not been constant; the conditions of the observations do not justify our making an assertion either pro or con.
Destruction of Living Matter.—As no certain answer is supplied by experiment, theory intervenes and gives two conflicting answers. The majority of physiologists are inclined to believe in the destruction of the living substance as the result of its own functional activity. The functional activity would therefore destroy not only the reserve-stuff, but also the protoplasmic material. This is the current view. Only this opinion is strongly challenged by the positive teaching of science. It is certain that this material, in the muscle, is but little attacked, if it is attacked at all. We have seen above that the physiologists, with Pflüger and Chauveau, are agreed on this point. The vital functional activity in particular is destructive to the reserve-stuffs. It does not destroy them much; it destroys the organic material still less. Both would be repaired in functional repose.
Growth of Living Matter.—The second assertion is diametrically opposed to this. Not only, says Le Dantec, is the muscle not destroyed in the functional activity, but it grows. Contrary to universal opinion, the protoplasmic material increases by activity, and it is destroyed in repose. There would thus be a general law—the law of functional assimilation. “A cell of brewers’ yeast when introduced into a sugared must makes this must ferment, and at the same time, so far from destroying it, it increases it. Now, the fermentation of the must is exactly the same as the functional activity of the yeast.” It is, says the same author, a mistake to believe that the phenomena of functional activity, of vital activity, only takes place at the price of organic destruction. Here, then, are these two competing views. They are not so very far apart as a matter of fact, since the question at issue is one of deciding between a slight destruction and a slight growth, but theoretically they are strongly opposed. Moreover, they are arbitrary, and experiment has not decided between them.