214 



Dr. A. Durig. A Contribution to 



[Nov. 20, 



tation, two almost instantaneous induction shocks, as nearly as 

 possible equal in strength, but opposite in direction, according to the 

 method first introduced by Bernstein and by Hermann in rheotome 

 experiments. The use of an instantaneous make and break contact 

 for the myograph and the introduction of a coil, suitably wound so as 

 to avoid induction, or of an incandescent lamp, into the primary 

 circuit, would have been a simple means of attaining this end. 



To fully acquaint the reader with what is new in the following 

 results, and with what is merely confirmatory of the observations of 

 others, that is to say of those of Waller, would make the present com- 

 munication too lengthy. I will, therefore, take it for granted that 

 Waller's researches, which form the starting-point of the subject, are 

 known. 



For the experiments on the eye the organ was kept either in day- 

 light or in the dark. The whole eyeball, or the special part of it that 

 was being investigated, lay in a slight depression of a kaolin (unpolaris- 

 able) electrode, and was connected by a thread of wick moistened in 

 physiological salt solution to the second electrode. The experiments 

 were always made on the freshly-removed eye, and so relate to Waller's 

 first stage only. A few observations were made on curarised frogs, 

 the optic nerve being exposed by the removal of part of the skull, and 

 looped round by a piece of wick to lead it off to the galvanometer. 

 Since a certain amount of bleeding ensued when the optic nerve was 

 cut, it was especially ascertained at the end of each such experiment 

 that the eye-circulation was maintained. In all the experiments 

 attached pieces of muscle and connective tissue were carefully removed 

 from the eyeball. 



The results obtained by the two measuring instruments, the galvano- 

 meter and the capillary electrometer, are fully in accordance with one 

 another • the responses to single induction shocks appear, however, dis- 

 tinctly smaller in the galvanometer than in the capillary electrometer. 

 In the latter instrument the effect exceeds the current of rest in 

 size, being more than twice and sometimes several times as great when 

 cornea and optic nerve are led off. Since the response to light stimu- 

 lation is hardly perceptible in the capillary electrometer, one sees at 

 once how considerable are the differences of potential of which the 

 " blaze currents" are the manifestation (Waller). 



Experiments on the whole Eyeball when the middle of the Cornea and the 

 cut end of the Optic Nerve are led off from. 



The cornea is always positive to the optic nerve. If the electrode is 

 moved away from the middle of the cornea nearer to the equator of 

 the eyeball, the current of rest becomes less, and if moved beyond 

 the equator to the posterior part of the eyeball it may be reversed. 



