486 



COMPARATIVE ELECTRO-PHYSIOLOGY 



subsequent depression of excitability at E is shown by the 

 upsetting of the balance downwards (fig. 293). 



I shall next take up the determination of the changes 

 induced by chemical agents on the excitability of plant nerve 

 and shall begin by describing the different effects which occur 

 on the application of calcium and potassium salts. For this 

 purpose, deci-molecular solutions were employed. Fig. 294 



shows the effect of CaCl 2 on 

 vegetable nerve, the solution 

 being applied at E on the 

 right-hand side. It will be 

 noticed that this caused an 

 upset of the balance, showing 

 an increase of excitability 

 that becomes considerable 

 after the expiration of five 

 minutes. In the case of KC1, 

 however, this effect was re- 

 versed, that is to say, a de- 

 pression was induced. This 

 is seen in fig. 295, where the 

 balanced record gives way, 

 first to diphasic, and after- 

 wards to a down-response, 

 indicating an effect of de- 

 pression at E. These two 

 of the basic moiety in in- 



FIG. 294. Photographic Record show- 

 ing Enhancement of Responsivity 

 by Application of CaCl 2 

 CaCl 2 applied to E is seen to exalt 



the responsivity of that point. 



experiments show the effect 



ducing changes of responsive excitability. 



I shall next describe experiments by which the simul- 

 taneous effects of two different reagents on the responsivity 

 of a given tissue may be compared. For this purpose, one 

 agent is applied at one end of the balance E, the other being 

 administered at E'. In the case of animal nerve, it was 

 shown by Griitzner, that both NaCl and NaBr induce ex- 

 citatory effects, that induced by NaBr being relatively the 

 greater. But the continued action of either of these reagents 



