526 COMPARATIVE ELECTRO-PHYSIOLOGY 



transmission in an isolated nerve. The conductivity, even 

 in the intact organism, we have seen to be liable to modifica- 

 tion from various factors such as fatigue, and it is easy to 

 understand that it will become still more fluctuating when 

 the conducting tissue is isolated. The inevitable changes 

 consequent on separation from the natural sources of energy 

 at once begin to take place. As the result of this sub-tonicity, 

 even a typically conducting tissue, like nerve, will cease to 

 be the conductor of true excitation, and there will then be, 

 properly speaking, no physiological distinction between such 

 a structure and a non-conducting tissue. By the absorption 

 of stimulus, however, a transformation sets in, and the non- 

 conducting becomes gradually reconverted, first, into a 

 feebly, and then into a very highly conducting structure. 

 The possible variations in conductivity, therefore, are not a 

 matter of some few units per cent, quantitatively, but even 

 considered qualitatively range from non-conductivity to the 

 highest conductivity. And even, further, when the nerve 

 has been once more rendered conducting, its velocity of 

 transmission will vary greatly with the tonic condition 

 conferred by previous stimulation. Over-stimulation, again, 

 by inducing fatigue, diminishes the power of conduction of 

 true excitation. This fact I shall be able to demonstrate by 

 special experiments. 



That such changes are not peculiar to the isolated nerve, 

 where the manifestation can be traced unmistakably to its 

 true cause, is seen in those cases of living animals where, 

 owing to mal-nutrition, or for other reasons, the tonic 

 condition of the nerve falls below par, with growing non- 

 conductivity and paralysis as the effect. And here it may 

 be said that the transformation again from non-conducting 

 or feebly-conducting to the normal state of conductivity 

 may in general be brought about by the same means as are 

 employed with the isolated nerve, namely, by the frequent 

 repetition of tetanising electric shocks. 



The photographic method of recording the response ot 

 nerve, employed in the Kunchangraph, has the advantage 



