102 



COMPARATIVE ELECTRO-PHYSIOLOGY 



The fact that the normal response of living tissues may be 

 reversed under fatigue, I am here able to show by an 

 experiment of an unexpected character. It is usually 

 supposed that fatigue is typical of such tissues as muscle, 

 and absent from nerve. But I shall show with regard to all 

 the various types of response, that there is none of these 

 which is distinctive of any one tissue. The difference is one 

 of degree and not of kind. The same intensity and duration 

 of stimulus which is efficient to cause 

 fatigue in muscle will not be enough to 

 do so in the case of nerve. But even 

 nerve will display fatigue when ex- 

 cessively stimulated. In the record given 

 in fig. 73, a particular nerve of frog 

 had been previously fatigued, by over- 

 stimulation, and on now taking individual 

 responses to individual stimuli, it was 

 found that they had become reversed to 

 positive. 



Thus a particular type of response is 

 the result of a particular condition of 

 the responding substance, and there is 

 none which is exclusively characteristic 

 of any one tissue. Were it otherwise, 

 ordinary muscle, in which the explosive 

 molecular change is supposed to be so 

 predominant, should typically show only 

 the fatigue, and never the staircase effect. But the following 

 record (fig. 74) shows that this is not the case. For at first 

 it exhibits a characteristic staircase effect ; the responses are 

 then for a time uniform ; and lastly, we see fatigue, in a 

 manner exactly corresponding to the theoretical considera- 

 tions which we have anticipated in stages B, C, and D. The 

 staircase response is thus not peculiar to cardiac muscle, but 

 is to be seen, under appropriate conditions, in skeletal 

 muscle, in nerve, and even in inorganic substances. In 

 fig- 75 is given a series of responses of Galena to Hertzian 



FIG. 73. Reversed Re- 

 sponse of Fatigued 

 Nerve 



