UNIFORM, FATIGUE, AND STAIRCASE EFFECTS 



107 



is to say, they consist of groups of responses, which wax and 

 wane alternately. 



Fatigue under continuous stimulation. — In connection 

 with the induction of fatigue under long-continued stimu- 

 lation, I shall now anticipate certain results regarding the 

 character of the responses given by matter universally — 

 results to be described in detail in the next chapter. It will 

 there be shown that if we represent a given molecular change, 

 caused by stimulus, as positive, the continuation of stimulus 

 will at first increase that change, until it has attained a 

 maximum, after which, under 

 the still continued action of the 

 same stimulus, there will be a 

 reversal or change to the nega- 

 tive. In a living tissue, then, 

 where the incidence of stimulus 

 causes contraction, we may be 

 prepared to find that the same 

 stimulus, long continued, will 

 bring about a reversal of this 

 effect, or, that is to say, a re- 

 laxation. 



In any case, such a reversal 

 is illustrated in the correspond- 

 ing phenomenon in contractile 

 muscle. It is there found 

 that, whereas the first effect of stimulus is contraction, the 

 same stimulus, when too long continued, brings about relaxa- 

 tion to the original form. In the electrical response of 

 plants under continuous stimulation, 1 also find this peculiar 

 fatigue-reversal (fig. 56J. 



I have also obtained similar fatigue- reversals in the longi- 

 tudinal response of radial organs. In fig. 56, (a), a series of 

 tetanic electric shocks was continuously applied during a 

 period of four minutes. The maximum contraction was 

 attained in the course of one minute, after which there was 

 a reversal, or relaxation. Under this condition of fatigue- 



FiG. 56. Rapid Fatigue under Con- 

 liuuous Stimulation in (a) Muscle ; 

 {/>) Leaf-stalk of Celery (Electrical 

 ixesponse) 



