474 



COMPARATIVE ELECTRO-PHYSIOLOGY 



between ordinary vegetable tissues and vegetable nerve, I 

 first studied its effect on the ordinary tissue of the petiole of 



Photographic Record of Effect of Ammonia on Ordinary 

 Tissue of Petiole of Walnut 



FIG. 283. 



Note that the effect of ammonia here is practically negligible. 



walnut. It will be seen from fig. 283 that ammonia here 

 induced practically no change in the excitability. But when 



the same reagent was applied 

 to the isolated nerve of 

 fern the response underwent 

 depression, followed by total 

 abolition, in the course of 

 five minutes (fig. 284). 



One very curious charac- 

 teristic of the electrical 

 response of frog's nerve is 

 the occurrence, as referred 

 to in the last chapter, of 

 three distinct types of re- 

 sponses, according to its 

 condition. Thus, as has 

 already been said, while 



Theresponsehere is rapidly diminished highly-excitable nerve ex- 

 and finally abolished. fo * 



hibits the normal negative 



response, the same nerve, when it has become sub-tonic, will 

 give a mixed or diphasic response ; and a nerve which is 



FIG. 284. Photographic Record of 

 Effect of Similar Application of 

 Ammonia on Plant-nerve 



