After the cessation of a briefly catalytic stimulus, not exceeding the physiological limit of intensity, another secondary result is observed, which is of the greatest importance for the continued existence of the living substance. The catalytic stimulus brings about a disturbance of the equilibrium of metabolism, which after cessation of the stimulus is reestablished by the living substance. In other words: recovery takes place. This fundamental principle has been known for a long time as the result of observation. If a skeletal muscle of our body has been activated for a prolonged period by nerve impulses, until it has become completely fatigued and incapable of work, a recovery takes place on the cessation of these impulses and the muscle is again capable of action. Likewise, as the result of strong mental activity during the day, we are mentally fatigued in the evening; recovery, however, occurs during the night, which results from the removal of the source of activity. The next morning finds us refreshed. This restitution occurs in every cell, and the return of its former capability of action, which had disappeared under the influence of stimulation, shows that compensation has taken place of the metabolism of rest, disturbed by the effects of the stimulus. Hering[54] has aptly termed this restitution as “the internal self-regulation of metabolism.” All recovery after disease is based on this self-regulation. The physician simply provides, by means of therapy, for the possibility of its taking place. Healing itself is brought about by the organism. “Natura sanat, medicus curat.”
Finally, a third kind of secondary effect of stimulation claims our interest. This is the secondary extension of the result of stimulation from the part of a living organism directly and primarily affected by the stimulus, to the surrounding structures. All living substance has the capability of conducting an excitation, which is produced locally through a catalytic stimulus, to a neighboring part, not directly affected by the stimulus. It finds its highest development in the nerve, but in no living structure is it completely absent. This capability has been frequently termed “conductivity of stimulation.” It is more precise, however, to speak of conductivity of excitation, for it is not the primary influencing external stimulus which is conducted in the living substance, but the excitation which it has produced. I have intentionally considered only the excitating effects of stimulation, and not those of the depressing reactions, as only excitations, not depressions, are conducted by the living substance. These questions, however, demand a closer analysis. Here we were concerned only with a survey of the general effects of stimulation. If I, therefore, once more summarize the results which have been gained, this is most clearly demonstrated by the following scheme:
Primary Effects of Stimulation
Excitation Depression
Functional Cytoplastic Functional
Secondary Effects of Stimulation
Secondary excitation Secondary depression
Conduction of excitation, Metamorphic processes, Self-regulation of metabolism
This, however, is simply a scheme, like all other schemes, having for its purpose a superficial survey of the subject.
It brings to some extent order into the overwhelming mass of manifold effects of stimulation but tells us nothing of the mechanism and genesis. Our further task must, therefore, be a more thorough analysis of this field.
CHAPTER V
THE ANALYSIS OF THE PROCESS OF EXCITATION
Contents: Indicators for the investigation of the process of excitation. Latent period. The question of the existence of assimilatory excitations. Dissimilatory excitations. Excitations of the partial components of functional metabolism. Production of energy in the chemical splitting up processes. Oxydative and anoxydative disintegration. Theory of oxydative disintegration. Dependence of irritability on oxygen. Experiments on unicellular organisms, nerve centers and nerve fibers. Restitution after disintegration by metabolic self-regulation. Organic reserve supplies of the cell. The question of a reserve supply of oxygen of the cell. Metabolic self-regulation as a form of the law of mass effect, and metabolic equilibrium as a condition of chemical equilibrium. Functional hypertrophy.