ARTIFICIAL RHYTHM. 199 
posing a large and sometimes a small portion of the 
tissue to the influence of the irritant. As I in- 
variably obtained the same result, there can be no 
doubt that in the case of chemical stimulation the 
artificial rhythm depends for its manifestation on 
the presence of a constant stimulus, and is not 
merely some kind of obscure fluttering motion 
which, having been started by a stimulus, is after- 
wards kept up independently of any stimulus. 
Such being the case, I naturally expected that if 
1 were to supply a constant stimulus of a thermal 
kind, I should also obtain the phenomena of arti- 
ficial rhythm. In this,. however, my expectations 
have not been realized. With no species of Medusa 
have I been able to obtain the slightest indication 
of artificial rhythm by immersing the paralyzed 
animals in heated water. I can only explain this 
fact by supposing that the stimulus which is sup- 
plied by the heated medium is of too uniform a 
character over the whole extent of the excitable 
tissues; it would seem that in order to produce 
artificial rhythm there must be a differential in- 
tensity of stimulation in different parts of the 
responding tissue, for no doubt even the excitatory 
influence of acidulated water is not of nearly so 
uniform an intensity over the whole of the tissue- 
area as is that of heated water. 
In now quitting the subject of artificial rhythm 
as it 1s manifested by the paralyzed bell of Sarsia, 
it is desirable again to observe that sustained 
artificial rhythm cannot be produced by means of 
chemical irritation in the case of any one of the 
