ARTIFICIAL RHYTHM. 211 
ing tissues. Now, I submit that my experiments 
have proved the former of these two theories inade- 
quate to explain all the phenomena of rhythm as 
it occurs in the Medusz; for these experiments 
have shown that even after the removal of the 
only ganglia which serve as centres of natural 
stimulation, the excitable tissues still continue to 
manifest a very perfect rhythm under the influence 
of any mode of artificial stimulation (except heat), 
which is of a constant character and of an inten- 
sity sufficiently low not to produce tetanus. And 
as I have proved that the rhythm thus artificially 
produced is almost certainly due to the alternate 
process of exhaustion and recovery which I have 
explained, there can scarcely be any doubt that in 
the natural rhythm this process plays an important 
part, particularly as we find that temperature and 
gases exert the same influences on the one rhythm 
as they do on the other. Again, as an additional 
reason for recognizing the part which the con- 
tractile tissues probably play in the production of 
rhythm, I have pointed to the fact that in the great 
majority of cases in which rhythmic action occurs 
the presence of ganglia cannot be suspected. For 
it is among the lower forms of life, where ganglia 
are certainly absent, and where the functions of 
stimulation and contraction appear to be blended 
and diffused, that rhythmic action is of the most 
frequent occurrence; and it is obvious with how 
much greater difficulty the resistance theory is here 
beset than is the one I now propose. Granted a 
diffused power of stimulation with a diffused power 
