ARTIFICIAL RHYTHM. 209 



suppose any other kind of difference to obtain, 

 either to the exclusion of this one or in company 

 with it. Such a supposition I now wish to suggest, 

 and it is this — that all rhythmical action being 

 regarded as due (at any rate in large part) to the 

 alternate exhaustion and restoration of excitability 

 on the part of contractile tissues, the reason why 

 continuous ganglionic stimulation produces incipient 

 tetanus in the case of some muscles and rhythmic 

 action in the case of others, is either wholly or 

 partly because the irritability of the muscles in 

 relation to the intensity of the stimulation is greater 

 in the former than in the latter case. If this sup- 

 position as to differential irritability be granted, 

 my experiments on paralyzed Aurelia prove that 

 tetanus would result in the one case and rhythmic 

 action in the other. For it will be remembered that 

 in these experiments, if the continuous faradaic 

 stimulation were of somewhat more than minimal 

 intensity, tetanus was the result; while if such 

 stimulation were but of minimal intensity, the 

 result was rhythmic action. Now, that in the 

 particular case of Sarsia the irritability of the toni- 

 cally contracting manubrium is higher than that 

 of the rhythmically contracting bell is a matter, 

 not of supposition, but of observable fact ; for not 

 only is the manubrium more irritable than the bell 

 in response to direct stimulation of its own sub- 

 stance, but it is generally more so even when the 

 stimuli are applied anywhere over the excitable 

 tissues of the bell. And from this it is evident 

 that the phenomena of muscular tonus, as they 



