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._” [54] _Ewald Hering_: “Zur Theorie der Vorgänge in der lebendigen Substanz.” In Lotos, Bd. 19, Prag. 1888.