THE MOLECULAR RESPONSIVENESS OF MATTER 



that when a substance is molecularly modified, the sign of 

 its response tends to be reversed. Thus, as already said, 

 ordinary silver gives positive, and modified silver, Ag', 

 negative response. But the latter, under strong and long- 

 continued stimulation, has its response re-converted, as it 

 were, to the normal positive. In the same way, under the 

 method of electro-motive variation also, we find the normal 

 positive response of, say, tin, or platinum, becoming con- 

 verted by molecular modification into negative, to be again re- 

 converted under continuous stimulation to the normal positive. 



There are, again, certain other substances, of which the 

 normal response is negative. Thus a wire of brominated 

 lead, for instance, when suitably prepared, is found to give an 

 electro-motive response in which the current flows from the 

 excited to the unexcited or away from the excited, the excited 

 point becoming galvanometrically negative. 



These electro-motive responses of the inorganic have thus 

 the same characteristics as those which have been observed 

 in the case of animal tissues. Certain tissues, such as highly 

 excitable muscle and nerve, give negative response that is 

 to say, the excited point 

 becomes galvanometrically 

 negative. Other tissues, 

 again, the skin for example, 

 give positive response. The 

 normal responses, moreover, 

 are sometimes found to be 

 reversed under molecular 

 modification, and to be re- 

 reversed to normal response 

 under long-continued stimu- 

 lation. 



The electrical responses 

 of metals, again, are subject 

 to an increase or decrease 



which is paralleled by the same phenomenon in the response 

 of animal tissues under similar circumstances. That is to 



FIG. 8. Fatigue in the Electric 

 Response of Metals 



