472 



Mr. G. J. Romanes on the [Jan. 11, 



strength of the current be suddenly increased after the maximum level 

 of a staircase has been attained by a feeble current, this level admits of 

 being slightly raised. Lastly, I find in Aurelia that the staircase action 

 is so pronounced that a stimulus which at the bottom of a staircase is 

 of less than minimal intensity, is able at the top of a staircase to give 

 rise to a contraction of very nearly maximum intensity. In such cases 

 no response is given to the first three or four stimuli. 



"With regard to this interesting staircase action, two questions natu- 

 rally present themselves. In the first place, we are anxious to know 

 whether the arousing effect, which is so conspicuous in a staircase series, 

 is due to the occurrence of the former stimulations or to that of the 

 former contractions ; and, in the next place, we should like to know 

 whether, during the natural rhythm of the tissue, each contraction exerts 

 a beneficial influence on its successor, analogous to that which may be so 

 certainly shown to occur in the case of contractions due to artificial sti- 

 muli. As regards the first of these questions, it is evident that the fact 

 of imdsible steps occurring at the bottom of a staircase (as just de- 

 scribed at the close of the last paragraph) proves that the staircase 

 effect, at any rate at its commencement, depends on the process of sti- 

 mulation as distinguished from that of contraction ; for, as in this case 

 the process of contraction does not occur at all, it clearly cannot have 

 any part in the production of the effect. JNTevertheless, that the process 

 of contraction does assist in producing the visible steps of the staircase, 

 is perhaps suggested by the result of the following experiment. Having 

 built up a staircase in the ordinary way, I suddenly transferred the elec- 

 trodes to the opposite side of the disk from that on which they rested 

 while constructing the staircase. On now throwing in another shock at 

 this part of the contractile tissue, so remote from the part previously 

 irritated, the response corresponded in all respects with the one pre- 

 viously given, i. e. it was a maximum response. This fact conclusively 

 proves that the staircase effect is a general one, pervading the whole 

 mass of the contractile tissue, and not confined to the immediate seat of 

 irritation*. 



The second of the above questions was answered by cutting an Aurelia 

 into a spiral strip of small width and great length, and removing all the 

 lithocysts save one. It was then observed that after the occurrence of 

 a natural pause of sufiicient duration, the first discharge only penetrated 

 a short way through the strip, the next a little further, the next further 

 still, and so on, till finally the contractile waves passed from end to end. 

 On now removing the ganglion and stimulating with successive induc- 



* Since tbis paper was sent in, Dr. Burdon-Sanderson has published some further 

 and highly interesting observations on Diontsa (see latest issue of the Proceedings of 

 the Eoyal Society). His results, as regards summation of stimuli and several other 

 points, are strikingly similar to my own ; but as I was not acquainted with them while 

 writing the text, I can only allude to them in this footnote. — [Jan. 10, 1877.] 



