1877.] 



Locomotor System of Medusa. 



475 



tissues when fresh : consequently, when the degree of this sensitiveness 

 is somewhat lowered by temporary exhaustion, the intensity of the sti- 

 mulation becomes somewhat less than minimal in relation to this lower 

 degree of sensitiveness. The tissue, therefore, fails to perceive 

 the presence of the stimulus, and consequently fails to respond. 

 But so soon as the exhaustion is completely recovered from, so soon will 

 the tissue again perceive the presence of the stimulation ; it will there- 

 fore again respond, again become temporarily exhausted, again fail to 

 perceive the presence of the stimulation, and therefore again become 

 temporarily quiescent. Now it is obvious that if this process occurs 

 once, it may occur an indefinite number of times ; and as the conditions 

 of nutrition, as well as those of stimulation, remain constant, it is mani- 

 fest that the responses may thus become periodic. 



In order to test this hypothesis, I made the following experiments. 

 Having first noted the rate of the rhythm under faradaic stimulation of 

 minimal intensity, without shifting the electrodes or altering the strength 

 of the current, I discarded the faradaic stimulation, and substituted for 

 it single induction- shocks thrown in with a key. I found, as I had 

 hoped, that the maximum number of these single shocks which I could 

 thus throw in in a given time, so as to procure a response to every shock, 

 corresponded exactly with the number of contractions which the tissue 

 had previously given during a similar interval of time when under the 

 influence of the faradaic current of similar intensity. For instance, to 

 take a specific case, it was found that under the faradaic current the rate 

 of the rhythm was one in two seconds. By now throwing in single shocks of 

 the same intensity, it was found that the quickest rate at which these 

 could be thrown in, so as to procure a response to every shock, was one 

 in two seconds. If thrown in at a slightly quicker rate, every now and then, 

 at regular intervals, one of the shocks would fail to elicit a response. The 

 length of these intervals, of course, depended on the rate at which the suc- 

 cessive shocks were thrown in ; so that, for instance, if they were thrown 

 in at the rate of one a second, the tissue would only, but always, respond 

 to every alternate shock. 



The following, and somewhat similar, experiment is still more conclu- 

 sive. As already stated, the rate of the artificial rhythm under faradaic 

 stimulation varies with the strength of the faradaic current. Well, by 

 choosing at random any strength of faradaic stimulation between the 

 limits where rhythmic response occurred, and by noting the rate of the 

 rhythm under that strength, I was generally able to predict the precise 

 number of single induction-shocks I could afterwards afford to throw in 

 with the same strength of current so as to procure a response to every 

 shock — this number, of course, corresponding exactly with the rate of 

 the rhythm previously manifested under the faradaic stimulation. 



Other experiments, which do not admit of being briefly detailed, ha^e 

 likewise confirmed the above hypothesis ; so I think the latter may be 



