48 JELLY-FISH, STAU-FISH, AND SEA-UllCllINS. 



venes imdor the inflaence 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 alread}^ published elsewhere.* Teta- 

 nus produced by faradaic electricity is not 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 

 streno-th 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 contracticms 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. 281-6. 



