48 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
venes under the influence of prolonged excitation. 
Moreover, I have obtained evidence of that polariza- 
tion of nerve-tissues under the influence of the 
constant current, which is known to physiologists 
by the term “electrotonus;” but it would be some- 
what tedious to detail the evidence on this head 
which I have already published elsewhere.* Teta- 
nus produced by faradaic electricity is net of the 
nature of an apparently single and prolonged con- 
traction, but that of a number of contractions 
rapidly succeeding one another, as in the case of the 
heart under similar excitation. This at least applies 
to Sarsia. In the case of Aurelia, tolerably strong 
faradization does cause a more or less well-pro- 
nounced tetanus. The continuity of the spasm is, 
indeed, often interrupted by momentary and partial 
relaxations. These interruptions are the more fre- 
quent the weaker the current ; so that, at a certain 
strength of the latter, the tetanus is of a wild and 
tumultuous nature; but with strong currents the 
spasm is tolerably uniform. That in all cases the 
tetanus is due to summation of contractions may 
be very prettily shown by the following experi- 
ment. An Aurelia is cut into a spiral strip, and all 
its lithocysts are removed ; single induction-shocks 
are then thrown in with a key at one end of the 
strip—every shock, of course, giving rise to a con- 
traction wave. If these shocks are thrown in at a 
somewhat fast rate, two contraction waves may be 
made at the same time to course along the spiral 
* See “Croonian Lectures,” 1875. Philosophical Transactions, 
vol. 166, part I. pp. 284-6. 
