Currents on Transmission of Excitation. 



507 



current is then a diminution, and that of a homodromous current an enhance- 

 ment of conductivity. 



The characteristic variations of conductivity induced in animal nerve by 

 the direction and intensity of current are in every way similar to those 

 induced in the conducting tissue of the plant. 



These various effects are demonstrated by the employment of not one but 

 various kinds of testing stimulus. Excitation may thus be caused (1) by 

 a single break-induction shock, or (2) a series of equi-alternating tetanising 

 shocks, or (3) by chemical stimulation, 



The results that have been given are only typical of a very large number, 

 which invariably supported the characteristic phenomena that have been 

 described. The records given in this paper are photographic reproductions 

 of the original. 



Conclusion. 



The action of an electrical current in inducing variation of conductivity 

 may be enunciated under the following laws, which are equally applicable to 

 the conducting tissue of the plant and the nerve of the animal. 



1. The passage of a current induces a variation of conductivity, the effect 

 depending on the direction and intensity of current. 



2. Under feeble intensity, heterodromous current enhances and homo- 

 dromous current depresses the conduction of excitation. 



3. The after-effect of a feeble current is a transient conductivity variation, 

 the sign of which is opposite to that induced during the continuation of 

 current. 



4. The normal conductivity variation undergoes a reversal under a 

 strength of current above the critical value. The heterodromous current 

 then induces a depression, while the homodromous current induces an 

 enhancement of conductivity. 



In my ' Researches on Irritability of Plants ' I have shown how intimately 

 connected are the various physiological reactions in the plant and in the 

 animal. And I ventured to predict that the recognition of this unity of 

 response in plant and animal will lead to further discoveries in physiology 

 in general. This surmise has been justified, for it was by the study of 

 effect of current on the conducting tissue of the plant that I was led to the 

 discovery of the characteristic effects of the direction of an electric current 

 on the conductivity of the animal nerve. 



My research assistants, Messrs. Guruprasanna Das, L.M.S., and Surendra 

 Chandra Das, M.A., rendered me very valuable help in this long investi- 

 gation. 



