Such are the instances to which one has up to the present applied the “all or none law.” The question if, as a matter of fact, such a condition has ever been realized in any living substance has until now found no final answer. Most authors, who accept the validity of the “all or none law” for certain living substances, do so with a certain reserve and speak only of the possibility or probability of such behavior. The subject has, however, as will be shown later, a great and even vital interest in another direction. For this reason I should prefer to postpone the treatment of the same to a later occasion. Here I wish simply to say, that _if_ the “all or none law” is valid in a strict sense for certain structures, then there exists no general constancy of the relations of the intensity of the stimulation and the amount of response, applicable to all living organisms. We will now return from this digression concerning the relations between the intensity of the stimulus and the response, to the further characterization of the properties of the stimulus. Besides the quality, the direction and the intensity of every alteration in vital conditions, an equally important factor is the duration of the alteration. The time relations, under which a deviation of the external vital conditions takes place, present immense and manifold variations in nature. In many cases the change is very complicated, as for instance, the alteration of the static pressure or the temperature under the influence of air or water currents, the osmotic pressure or chemical factors in diffusion currents, and the light intensity produced by the movement of clouds. These very irregular alterations have practically little interest for us. Here we are concerned rather with the differentiation of the time alterations of the processes of the simplest fundamental types, which are of importance in studying the course of the reaction. For it is of such simple elements that the complicated and irregular alterations of the above-mentioned kinds are composed.