DIFFERENT TYPES OF RESPONSE 1 23 



converted into the molecular red, or allotropic variety. This 

 molecular change, however, is also attended by a concomi- 

 tant change in the chemical activity, phosphorus in the red 

 condition being less active chemically than in the yellow. 



Under certain circumstances, further, it is possible to 

 have a secondary series of chemical events following upon a 

 condition of unequal molecular strain. We have seen that a 

 homogeneous living tissue, when unstimulated, is iso-electric. 

 When stimulated, however, an electromotive difference is 

 induced, as between the more and the less acted parts of 

 the tissue. The result is an electrical current attended by 

 chemical changes. As a consequence of such volta-chemical 

 action, when prolonged, by-products (fatigue-stuffs?) may be 

 accumulated, and these may have a depressing effect on the 

 activity of the tissue. Hence, just as after very prolonged 

 activity of a voltaic element it is necessary to renew the 

 active element and change the electrolyte surcharged with 

 by-products, so, after sustained activity of a living tissue, 

 the process of renewal, or renovation, will be necessary. 

 Thus we see how, upon the fundamental molecular derange- 

 ment, a chain of very various chemical events may follow as 

 its after-effect. And it is only by going in this way to the 

 very root of the phenomenon, that we can avoid the many 

 contradictions with which we are confronted by the chemical 

 theory. 



I have therefore aimed at demonstrating the universal 

 existence in matter of the property of responsiveness, and 

 by taking the simplest cases and excluding as many com- 

 plicating factors as possible, have attempted to show further 

 how this power of response is modified by those conditions 

 which occasion fatigue, or its converse, the staircase effect. 

 Having thus cleared the ground, it is possible to take up 

 cases of greater complexity. 



Different modes of transformation of stimulus. — It has 

 been assumed that response is brought about by a sudden 

 explosive chemical change, the stimulus acting as if on a 

 trigger, for the release and run-down of potential chemical 



