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 
