THEORY OF THE BREAK-CONTRACTION. 51 



Analogy, however, does not necessarily imply identity. Though 

 we may point to phenomena in other provinces similar to those 

 with which we have become acquainted in studying the action 

 of the current on nerves, we cannot regard the two as equivalent ; 

 nor form by their aid any sufficient and complete theory of the 

 phenomena which occur at the moment that the current is closed 

 and during the period of its flow along a nerve. Yet these analogies 

 and others of a like kind are perhaps not without value, since at 

 any rate they suggest a possibility, however slight, of getting 

 beyond the bare facts of experiment. 



It is quite otherwise with the break-excitation and with the 

 other phenomena attending opening of the current. We can, so 

 far as I know, point to no similar facts in other provinces of know- 

 ledge, and Pfliiger's famous formula, that the disappearance of 

 anelectrotonus stimulates, is merely a very precise and exact word- 

 ing of the facts. It states, however, nothing more, and advances 

 us not one step towards understanding the essence of the pheno- 

 menon. Even at the earliest period in the history of electro- 

 physiology, the break-contraction had arrested the attention of 

 enquirers; and even Volta attempted to find for it a theoretical 

 explanation. Neither he nor his followers, however, succeeded in 

 presenting a theory which satisfied the requirements of science; 

 and his views, as well as those of PfafF, Lehot, Erman, Marianini, 

 and the earlier ones of Matteucci, can now claim merely an historical 

 interest \ 



Peltier, whose views appear to be more important than these, 

 explains the break-contraction in direct contraction as due to 

 the polarisation of the muscle, expressing himself thus : ' On doit a 

 M. Hitter ' he says ' puis a M. De La E/ive la connaissance de ce 

 fait ; qu'un arc metallique, formant un circuit hydroe'lectrique par 



current is led from the eye in the same way, there occurs at once a copious disengage- 

 ment of gaseous bubbles, and, if the eye has been previously exposed to the action of 

 the in-going current, there occurs usually a manifest diminution of the clouding and 

 of the coagulum, both of which nearly disappear in a few weeks, especially if the 

 experiment is accompanied with only a slight amount of inflammation ' (pp. 11-19). 



I repeated the experiment in the following way. I used a battery of 5 or 6 

 Meidinger's elements. When I applied the positive pole to the cornea of a frog 

 which had just been killed, and the negative to any part of the trunk, after a few 

 moments there appeared a distinct clouding of the cornea. When I changed the 

 direction of the current, so that the negative pole rested on the cornea, there was at 

 once a copious disengagement of minute bubbles of gas ; these being removed, the 

 cornea appeared almost as clear and transparent as at first. 



1 See the complete account by du Bois-Keymond, Untersuchungen iiber thierische 

 Elektricitat, Berlin, 1848, pp. 307-402. 



E 2 



