216 



Dr. A. Durisj. A Contribution to 



[Nov. 20. 



When the one leading-off electrode is moved away from the cornea 

 towards the equator of the eyeball, not only is the difference of 

 potential between the two poles diminished, but also the effect pro- 

 duced by an induction shock, which was before considerable, has 

 now almost vanished. Instead of an excursion extending; over 

 600 divisions it now extends over only 20 or 30, and its direction 

 occasionally varies with that of the induction current. When the 

 electrode is replaced on the cornea the original large deviation is again 

 produced in response to stimulation. 



When the breaking of the second contact by the myograph lets the 

 preparation into the capillary electrometer, two different main types of 

 response may be distinguished by the form of the observed effect. 

 The curve is either distinctly diphasic, the first phase being nega- 

 tive, i.e., in the opposite direction to the resting current, and the 

 second, which is always considerably stronger, being positive and 

 lasting for a much longer time ; or a purely monophasic vari- 

 ation is obtained which is always positive. The negative part of 

 the diphasic variation was so soon over that when, by means of a 

 turn-over key, the preparation was connected with the galvanometer 

 by hand instead of by the myograph, the most that could be observed 

 as the last trace of the first phase was, on account of the rela- 

 tively great inertia of the galvanometer, an excursion of a few 

 divisions only, by reason of the relatively great inertia of the 

 galvanometer. The phenomenon of the diphasic effect occurs when 

 the induction currents— especially break-shocks — are in the same 

 direction as the " blaze current " is expected to be in, which suggests 

 that one is here dealing with pure polarisation phenomena which do 

 not show themselves when the exciting current is in the opposite 

 direction, as the two effects are then in the same direction. Experi- 

 ments with this in view are needed to make the matter clear. Xo 

 explanation has, so far as I am aware, been offered before of the 

 occasional absence of the first phase, which, if it is merely a polarisation 

 effect, must be a physical change independent of any processes in 

 living tissue. 



Faradisation produces a distinct augmentation of the resting 

 current, which, however, varies greatly in size and duration in 

 different preparations. Break and make induction shocks in either 

 direction are effectual after faradisation, and produce positive 

 variations which appear as an increase of the augmentation. It is 

 only after very strong faradisation that single induction shocks 

 are ineffectual; in this case the initial augmentation of the pre- 

 existing current (due to the faradisation) soon begins to disappear, 

 the diminution continuing until a resting current in the opposite 

 direction is produced. 



The fact that the effects of excitation are so small when the equator 



