TRANSACTIONS OF THE SECTIONS. Kil 



supplying a coustaul stiinuhitiu)i—{\ie rhijthm loeing supposed due to the ^ame cause.? 

 as is the artificial rhythm of AurvUa aiirifa. From this it will bo .«oeu th.at the 

 essential point of dillereuce between the cuiTent theory of rhythm as due to ganglia 

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

 the acciamilation of energy bj' ganglia to be a continuous process, the resistauce 

 theoiy supposes the discharr/e of this accumulated energy to be intermittent, while 

 the exhaustion theory supposes it to be continuous. According to the former 

 theory, therefore, the rhythm results because the stimulation is periodic ; according 

 to the latter theory, the rhythm results because the alternate process of exhaustion 

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



Without waiting to discuss the it priori merits of these rival theories, the author 

 proceeded at once to mention some further experiments v,-hich were designed to 

 test the new theory, and which have so far confirmed it as to show the causes which 

 modify the natural rhythm of Aurelia likewise modify, in the same ways antl 

 degrees, the artificial rhythm. 



(ff) Other modes of constant stimulation, besides that supplied by favadaic elec- 

 tricitj', likewise cause rhythmic action on the part of the deganglionated tissues of 

 MedusK. For instance, the voltaic curreut causes this action * ; and dilute 

 chemical stimuli tend to produce the same effect. 



(h) With each increment of temperature the rate of the artificial rhythm in- 

 creases suddenl}', just as it does in the case ofthe natural rhythm. Moreover, there 

 seems to be a sort of rough correspondence between the amount of iufluence that 

 any given degree of temperature exerts on the rate of the natural and ofthe artificial 

 rhythm respectively. Further, it will be remembered that in warm v.-ater the 

 natural rhythm, besides being cj^uicker, is not so regular as it is in cold water : thus 

 also it is with the artificial rhythm. Lastly, water below 20'^ or above ^■o^ sus- 

 pends the natural rhythm ; and the artificial rliytlim is suspendol at about the 

 same degrees. 



(c) Carbonic acid retards and eventually su.■^pends the artificial rhytlnn, in just 

 the same way as this gas acts on the natural rhj'thm. 



(f?) When the marginal ganglia of Sarsia are removed, the manubrium shortly 

 afterwards relaxes to five or six times its normal length. There can be no doubt 

 that this eft'ect is due- to the muscular fibres of the manubrium having been pre- 

 viously kept in a state of tonic contraction by means of a coutiiiuous ganglionic 

 discharge from the margin. Now physiologists are unanimous in regarding mus- 

 cular tonus as a kind of gentle tetanus due to a persistent ganglionic stimul.ntion ; 

 and against this opinion nothing can be said. But, in accordance with tlie ac- 

 cepted theory of ganglionic action, physiologists further suppose that the only 

 reason why some muscles are thrown into a state of tonus by ganglionic stimula- 

 tion, while other muscles are thrown into a state of rhythmic action by the same 

 means, is because the rei-i^fance to tlie passage of the stimulation from the ganglion 

 to the muscle is less in the former than in the latter case. On the other hand, tlie 

 new theory of ganglionic action explains the diflerence by supposing a difttireut 

 degvec ol irritabilifi/ on the part of the muscles in the two cases; for it will be 

 remembered that in the author's experiments on paralyzed AurcUn, if the continuous 

 stinuilation were of somewhat more than minimal intensity, tctaiuis was the result, 

 while if such stimulation were but of minimal intensity, the result was rhythmic 

 action. Now the author finds in the case of Sarsia that the muscular tissue ofthe 

 manubrium is more excitable than th.o muscular tissue of the bell ; so that, for this 

 and other reasons, the facts here accord more closely with the exhaustion than 

 with the resistance theoiy of ganglionic action. 



licflex Action. — The occurrence of reilex action in the Medusai is of a vi'ry marked 

 character. For instance, if the manubrium be irritated, the swimming-organ re- 

 sponds to the irritation by giving one or more contractions; but if tlie marginal 

 ganglia be now removed, the swimming-organ no longer responds even to the most 

 violent u'ritation. Again, in Aurelia, if only one litliocyst be Ifft in fifti, and if, 

 during a pause in the activity of the latter, any part of the irritable surface of the 



* Thus far the results arc strikincrly similar to those obtained hy Dr. For*ter iu (Ii# 

 case of the lieart-apex. 



