THE CHARACTERISTICS OF STIMULI 61 



It is sometimes the case that under the influence of a stimulus 

 a new equilibrium is developed, which may remain as long as 

 the stimulus persists. This most frequently occurs as a result 

 of weak stimuli. That which is usually termed "individual 

 adaptation" belongs in this category. Likewise some of the nat- 

 ural and artificial immunizations may also be included. The con- 

 tinued stimulation in such cases of adaptation as we learned 

 before in the example of Amoeba Umax and radiosa or Branchipus 

 stagnalis and Artemia salina becomes a vital condition for the 

 living substance in its new state. 



The other result, namely, that of death ensuing sooner or 

 later, is most frequently produced by stronger stimulation. 

 Through the effect of the prolonged stimulation, the change in 

 the living system is so great that all harmonious interaction of 

 the various processes of life become after a time impossible. 

 The disturbance of this equilibrium after a longer or shorter time 

 becomes so great that life ceases. By far the greater number of 

 all diseases furnish examples of this kind. Disease is nothing 

 else but reaction to stimulation. Should a constant stimulus per- 

 sist and if the development of a new equilibrium of this system 

 is not established, the result is premature death. 



In most cases, as, for instance, the nerve impulses which move 

 toward an organ, or better still the electrical stimuli as used for 

 experimental purposes, it is not a question of a permanent but 

 of a temporary alteration in the external vital conditions. The 

 stimulus starts, then ceases after a longer or shorter period. In 

 this way there is added to the deviation at the start also the altera- 

 tion at its termination. The latter takes place with different 

 degrees of rapidity, in a manner analogous to that of the initial 

 alteration, and can bring about response. With this the curve 

 of the duration of the course of the stimulus becomes somewhat 

 more complicated and in consequence a like effect is observed in 

 the response. The "making," duration and "breaking" of the 

 constant current furnishes the example of this type. The 

 "making" of the current being a quick alteration calls forth a 

 strong and sudden excitation (in the muscle contraction) ; the 

 continuation of the current maintains weak excitation of equal 



