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 Medusae ; 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 1 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 cei-tainly 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 

 dififused power of stimulation with a diffused power 



