476 



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



considered almost as demonstrated. Upon this hypothesis, therefore, I 

 have constructed a theory concerning the rhythmic action of organic 

 tissues in general. The details of this theory cannot be rendered in 

 the present abstract ; but in its main outlines it is very simple, "sdz. 

 that all such rhythmic action is due to the alternate process of exhaus- 

 tion and recovery of contractile tissues, which has just been explained. 

 Therefore the particular case of rhythmic action of ganglionated tissues 

 is supposed by this theory to be due, not to any special resistance 

 mechanism on the part of the ganglionic tissues, but to the primary 

 qualities of the contractile tissues. In other words, the function of the 

 ganglia is supposed to be merely that of supplying a constant stimulation, 

 the rhythm being supposed due to the same causes as is the artificial 

 rhythm of Aurelia aurita. Prom this it will be seen that the essential 

 point of difference between the current theory of rhythm as due to 

 ganglia and the theory now proposed consists in this — that whereas both 

 theories suppose the accumulation of energy by ganglia to be a continuous 

 process, the resistance theory supposes the discharge of this accumulated 

 energy to be intermittent, while the exhaustion theory supposes it to 

 be constant. Accordiug to the former theory, therefore, the rhythm 

 results because the stimulation is periodic ; according to the latter theory, 

 the rhj^hm results because the alternate process of exhaustion and 

 recovery, or the fall and rise of excitability, is periodic. 



Without here waiting to discuss the a ]}riori merits of these rival 

 theories, I will proceed at once to mention some further experiments 

 which were designed to test the new theory, and which have so far con- 

 firmed it as to show that the causes which modify the natural rhythm of 

 Aurelia likewise modify, in the same ways and degrees, the artificial 

 rhythm. 



(a) Other modes of constant stimulation besides that supplied by f aradaic 

 electricity likewise cause rhythmic action on the part of the degangiio- 

 nated tissues of Medusae. As stated in my former paper, the voltaic 

 current causes this action*; and, as stated in an earlier part of this ab- 

 stract, dilute chemical stimuli, and even mechanical irritation, tend to 

 produce the same effect. Again, the remarkably sustained rhythmic 

 motion which is manifested by the paralyzed bells of Sarsia in acidulated 

 water, which last year appeared so anomalous, is clearly to be referred to 

 the same category. 



(b) As regards the effect of temperature on the rate of the artificial 

 rhythm, it is only necessary to state the following details. "With each incre- 

 ment of temperature the rate of the artificial rhythm increases suddenly, just 

 as it does in the case of the natural rhythm. Moreover, there seems to be a 

 sort of rough correspondence between the amount of influence that any 

 given degree of temperature exerts on the rate of the natural and of the 



* Thus far the results are strikingly similar to those obtained by Dr. Foster in the 

 case of the apex of the heart. 



