84 COMPARATIVE ELECTRO-PHYSIOLOGY 



may also be demonstrated by subjecting the tissue to con- 

 tinuous stimulation or tetanisation, when the abnormal 

 positive is found to pass into normal negative. 



From the experiments that have been described, it would 

 appear that the several kinds of response characteristic of 

 various tissues are relatively rather than absolutely different. 

 The true excitatory reaction of an excitable tissue, is one 

 of galvanometric negativity. Any diminution of the ex- 

 citability whether by lowering of tonic condition or other 



FIG. 54. Photographic Record of Abnormal Positive passing into Normal Nega- 

 tive Response in a Withered Specimen of Leaf-stalk of Cauliflower 



Stimulus was gradually increased from I to 10, by means of spring-tapper. 

 When the stimulus intensity was 10, the response became reversed into 

 normal negative. (Parts of 8 and 9 are out of the plate.) This record 

 is to be read from right to left. Down-records stand for positive, and 

 up-curves for negative responses. 



causes will bring about a decrease of this negativity, which 

 may culminate in actual positivity. Thus negative is not 

 separated from positive response by any break of continuity ; 

 but we are able, on the contrary, to trace a gradual transition 

 from one to the other. Moreover, in every response we 

 have the two antagonistic elements, positive and negative, 

 either actually or potentially present. The form taken by 

 the resultant response is entirely determined by the question 

 of what proportion of the stimulus impinging upon the tissue 

 becomes latent ; and this in its turn depends upon the tonic 



