520 COMPARATIVE ELECTRO-PHYSIOLOGY 



a result of this, the abnormal positive will pass into normal 

 negative response, through an intermediate diphasic, after 

 the impact of a series of stimuli, or after tetanisation. The 

 enhancement of conductivity and excitability thus conferred 

 on the tissue by the absorbed stimulus will now act by 

 still further tetanisation, to bring about the enhance- 

 ment of the normal negative response. Starting thus, 

 with the most depressed condition of the tissue, and sub- 

 jecting it to continuous action of stimulus, we obtain four 

 typical stages : (i) the abnormal, passing after short tetanisa- 

 tion into (2) the diphasic ; this in its turn giving place to 

 (3) the normal negative alone ; which finally becomes (4) the 

 enhanced negative. 



In studying electrical response, both of animal and vege- 

 tal nerves, under appropriate experimental conditions, we 

 have already seen various examples of these different types 

 of response and their transformations. But under such modes 

 of experiment as have been described, the effects were, as 

 already stated, due to joint changes in excitability and con- 

 ductivity. I shall now, however, describe a still simpler 

 experimental arrangement, in which the stimulus is applied 

 directly on the tissue, and the responsive variations are, 

 therefore, due to variations in the excitability alone. These 

 changes, moreover, will be recorded by means of their direct 

 mechanical expression, namely, contraction, or its opposite 

 expansion. 



With regard to abnormal response, I have already stated 

 that this is brought about, not by ' staleness,' or the moribund 

 condition, with its concomitant chemical changes, but by 

 the run-down of the energy of the tissue in isolation. On 

 investigating this subject, by means of mechanical response, 

 with its superior sensitiveness, this conclusion finds inde- 

 pendent support of the strongest character. On taking 

 even the freshest specimen, I generally find that its 

 responses at first are the abnormal positive. These gradually 

 pass into moderate negative through diphasic. This is due 

 to the raising of the tonic condition by the absorption of 



