i 4 o RESPONSE IN THE LIVING AND NON-LIVING 



which may affect one kind of tissue and not others. 

 Poisons in general may be regarded as extreme cases of 

 depressants. As an example of those which produce 

 moderate physiological depression, potassium bromide 

 may be mentioned, and this also diminishes electric 

 response. There are other chemical reagents, on the 

 other hand, which produce the opposite effect of increas- 

 ing the excitability and causing a corresponding exalta- 

 tion of electric response. 



We shall now proceed to inquire whether the re- 

 sponse of inorganic bodies is affected by chemical 

 reagents, so that their excitability is exalted by some, 

 and depressed or abolished by others. Should it prove 

 to be so, the last test will have been fulfilled, and 

 that parallelism which has been already demonstrated 

 throughout a wide range of phenomena, between the 

 electric response of animal tissues on the one hand, and 

 that of plants and metals on the other, will be com- 

 pletely established. 



Action of stimulants on metals. We shall first study 

 the stimulating action of various chemical reagents. 

 The method of procedure is to take a series of normal 

 responses to uniform stimuli, the electrolyte being water. 

 The chemical reagent whose effect is to be observed is 

 now added in small quantity to the water in the cell, 

 and a second series of responses taken, using the same 

 stimulus as before. Generally speaking, the influence 

 of the reagent is manifested in a short period, but there 

 may be occasional instances where the effect takes some 

 time to develop fully. We must remember that by the 

 introduction of the chemical reagent some change may 



