The most important factor to be considered in producing the response to variations of intensity, is not the _absolute rapidity_, but rather the _relative rapidity_; that is, the rapidity in relation to the characteristic rapidity of reaction of the particular living substance concerned. The rapidity of the reaction to stimuli is very different in various forms of living substance. On the one hand, we have forms reacting very quickly, as the nerve and the striated muscle; on the other, those which respond very slowly, such as a great number of unicellular organisms. Between these are a great number of living substances which, as far as the rapidity of the reaction is concerned, occupy intermediate positions of every varying degree. It is clear that the adequate stimuli for slowly reacting substances must be those having also a slow change of intensity; for quickly reacting, those having a rapid change of intensity.[33] If a nerve muscle preparation is simulated with the single induction shock, the “break” as well as the “make” shock has effect. But even here a difference is noticeable. The “make” shock has a weaker effect than the “break” shock. This difference is due to the difference of abruptness in its course, which when the current is made is less than that of opening, for, when the current is made, the ascent of the primary current is retarded by the extra current flowing in the opposite direction, whereas, when broken, with the fall of the intensity of the primary current, the extra current in the primary coil flows in the same direction. In consequence of this there is a perceptible difference in the rapidity of the alteration of the “make” and “break” shocks. (Figure 4.) [33] Vergl. _Julius Schott_: “Ein Beiträg zur electrischen Reigung des quergestreiften Muskels von seinen Nerven aus.” Pflügers Archiv Bd. 48, 1891. [Illustration: Fig. 4. Course of induction shocks. 1 and 2 make and break of the primary current. 1_{1} and 2_{1} make and break induction shocks. (After _Hermann_.)]