474 



Mr. G. J. Romanes on the 



[Jan. 11 



are thrown in at a still faster rate, so as to diminish the distance between 

 any two successive waves, a point soon comes at which every wave over- 

 takes its predecessor, and, if several waves be thus made to coalesce, the 

 whole strip becomes throvrn into a state of persistent spasm. In such 

 experiments it is interesting to observe that, no matter how long the 

 strip may be, or how complicated the time-relations between the succes- 

 sive stimuli are made, whatever disturbances are set up at one end of the 

 strip are faithfully transmitted to the other. This of course shows that 

 the rate of transmission is so identical in the case of all the stimuli 

 originated, that the sum of the effects of any series of stimuli is dehvered 

 at the distal end of the strip, with all its constituent parts as distinct 

 from one another as they were at starting from the proximal end of the 

 strip. 



(C) Artificial rliytlim. — When the swimming-organ of Aurelia has been 

 paralyzed by removal of its lithocysts, and is then subjected to faradaic 

 stimulation of minimal intensity, the response it gives is not tetanic, but 

 strictly rhythmic. The rate of the rhythm varies in different specimens, 

 but usually corresponds with that of rapid swimming. The artificial 

 rhythm may be obtained with a portion of any size of irritable tissue, and 

 whether a small or a large piece of the latter be included between the 

 electrodes. 



Progressively intensifying the strength of the faradizing current] has 

 the effect of progressively increasing the rate of the artificial rh}i;hm up 

 to the point at which the rhythm begins to pass into tetanus due to 

 summation of the successive contractions. But between the slowest 

 rh}^hm obtainable by minimal stimulation, and the most rapid rhythm 

 obtainable before the appearance of tetanus, there are numerous degrees 

 of rate to be observed. 



The persistency of any given rate of rhythm under the same strength 

 of current is wonderfully great ; for it generally requires more than an 

 hour of continuous faradization before the rhythm begins to become ir- 

 regular, owing to incipient exhaustion. At first only one systole is 

 omitted at long intervals ; but afterwards these omissions become fre- 

 quent and all the contractions irregular. Finally the contractions cease 

 altogether ; but a prolonged rest of half an hour or an hour restores the 

 irritability. 



The hypothesis by which I explain this artificial rhythm (a rhythm 

 which in most cases is quite as regular as that of a heart) is as follows. 

 Every time the tissue contracts it must, as a consequence, suffer a cer- 

 tain degree of exhaustion, and therefore must become slightly less sen- 

 sitive to stimulation than it was before. After a time, however, the 

 exhaustion will pass away, and the original degree of sensitiveness will 

 thereupon return. Now the intensity of the faradaic stimulation, which 

 is alone capable of producing rhythmic response, is either minimal or 

 but slightly more than minimal in relation to the sensitiveness of the 



