THE CHARACTERISTICS OF STIMULI 51 



Such are the instances to which one has up to the present 

 appHed the "all or none law." The question if, as a matter of 

 fact, such a condition has ever been realized in any living sub- 

 stance has until now found no final answer. Most authors, who 

 accept the validity of the "all or none law" for certain living sub- 

 stances, do so with a certain reserve and speak only of the possi- 

 bility or probability of such behavior. The subject has, how- 

 ever, 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 rela- 

 tions 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 altera- 

 tion in vital conditions, an equally important factor is the dura- 

 tion of the alteration. The time relations, under which a devia- 

 tion 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 move- 

 ment 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. 



The simplest form of an individual change in the external 

 vital conditions would be a regular and constant alteration of 

 intensity which can be graphically represented as a straight line, 

 wherein the intensities are the ordinates and the time the abscissa. 



