ARTIFICIAL RHYTHM. 201 



as distinguished from the contractile tissues, and I 

 have founded this belief principally on the facts 

 which have now been stated, and which certainly 

 prove at least this much : that after the removal of 

 the centres of spontaneity, the contractile tissues 

 of the Medus?e display a marked and persistent 

 tendency to break into rhythmic action whenever 

 they are supplied w^ith a constant stimulus of feeble 

 intensity. Without waiting again to indicate how 

 this fact tends to suggest that the natural rhythm 

 of the unmutilated organisms is probably in large 

 part due to that alternate process of exhaustion 

 and restoration of excitability on the part of the 

 contractile tissues, whereby alone the phenomena 

 of artificial rhythm can be explained,* I shall go 

 on to describe some further experiments which were 

 designed to test the question whether the influences 

 which affect the character of the natural rhythm 

 likewise, and in the same manner, affect the 

 character of the artificial rhythm. I took the 

 trouble to perform these experiments, because I felt 

 that if they should result in answering this question 

 in the affirmative, they would tend still further to 



* It is of importance to point out the fact that some of my 

 previously stated experiments appear conclusively to prove that 

 the natural stimulation which is supplied by the marginal ganglia 

 of the Medusae resembles all the modes of artificial stimulation 

 which are competent to produce artificial rhythm in one im- 

 portant particular; the intensity of the stimulation which the 

 marginal ganglia supply is shown by these experiments to be 

 about the same as that which is required to produce artificial 

 rhythm in the case of artificial stimulation. In proof of this 

 point, I may allude particularly to the observations which are 

 detailed on pp. 134-136. 



