A?.TIFICIAL RHYTHM. 179 



Any such merely mechanical source of fallacj" 

 being thus, I think, excluded, we are compelled to 

 regard the facts of artificial rhythm as of a purely 

 physiological kind. The question, therefore, as to 

 the explanation of these facts becomes one of the 

 liighest interest, and the hypothesis which I have 

 framed to answer it is as follows. Every time the 

 tissue contracts it must as a consequence suffer a 

 certain amount of exhaustion, and therefore must 

 become slightly less sensitive to stimulation than 

 it was before. After a time, however, the ex- 

 haustion will pass away, and the original degree 

 of sensitiveness will thereupon return. Noav, the 

 intensity of faradaic stimulation which is alone 

 capable of producing rhythmic response, is either 

 minimal or but slightly more than minimal in 

 relation to the sensitiveness of the tissue when 

 fresh ; consequently, when this sensitiveness is 

 somewhat lowered by temporary exhaustion, the 

 intensity of the stimulation becomes somewhat less 

 than minimal in relation to this lower degree of 

 sensitiveness. The tissue, therefore, fails to perceive 

 the presence of the stimulus, and consequently fails 

 to respond. But so soon as the exhaustion is com- 

 pletely recovered from, so soon will the tissue again 

 perceive the presence of the stimulus ; it will there- 

 ibre again respond, again become temporarily ex- 

 hausted, again fail to perceive the presence of the 

 stimulus, and again become temporarily quiescent. 

 Now it is obviou.i tluit if this process occurs once, 

 it may occur an iudoiinite number of times; and 

 as the conditions of nutrition, as well as those of 



