EXCITABILITY UNDER CHEMICAL REAGENTS 



135 



effect of the reagent on both receptivity and responsivity 

 jointly. 



If, however, we wish to study the effect of the reagent on 

 responsive excitability alone, it will be necessary to separate 

 the receptive from the responding point, and apply the reagent 

 on the latter. This may be done by the method of trans- 

 mitted stimulation described previously. Successive uniform 



Before f After 



FIG. 93. Photographic Record showing the nearly complete Abolition 

 of Response by strong KOH 



The two vertical lines are galvanometer deflections due to ! volt, before 

 and after the application of reagent. It will be noticed that the total 

 resistance remains unchanged. 



stimuli applied at a given point cause excitatory response at 

 the separate responding point, the record of which is taken ; 

 after this, the chemical reagent is applied locally at the 

 responding point. It will be seen that the receptive 

 excitability and the conductivity of the intervening tissue 

 remain unaffected, changes being induced at the responding 

 area alone. 



I shall now describe effects obtained by this method. 



