ARTIFICIAL RHYTHM. 189 
persistent rhythm admits of being produced by 
this means. In this particular species, the manu- 
brium never exhibits any spontaneous motion after 
the ganglia of the nectocalyx have been removed. 
But if it be nipped with the forceps, or otherwise 
irritated, it contracts strongly and suddenly; it 
then very slowly and gradually relaxes until it has 
regained its original length. After a considerable 
interval, and without the application of any addi- 
tional stimulus, it gives another single, sudden, 
though slight contraction, to be again followed by 
eradual relaxation and a prolonged interval of 
repose, which is followed in turn by another con- 
traction, and so on. These sudden and well-marked 
contractions occur at intervals of many seconds, 
and show a decided tendency to rhythmic periodi- 
city, though the rhythm is not always perfectly 
exact. This intensely slow rhythm, as the result 
of injury, may continue for a long time, particu- 
larly if the injury has been of a severe character. 
There can be no doubt, therefore, that the mecha- 
nical (or other) injury in this case acts as a source 
of constant irritation; so that here again we have 
evidence of rhythmic action independent of ganglia, 
and caused by the alternate exhaustion and re- 
covery of contractile tissues.* 
* We may pretty safely conclude that ganglia are altogether 
absent in the manubrium of Sarsia, not only because Schultz 
has failed to detect them in this organ microscopically, but also 
because of the complete absence of spontaneity which it mani- 
fests. I may here mention that this case of the manubrium of 
Sarsia is precisely analogous to another which I have observed in 
a widely different tissue, namely, the tongue of the frog. Here, 
