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 Medusze display a marked and persistent 
tendency to break into rhythmic action whenever 
they are supplied with 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 Medusze 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. 
