1902.] 



the Question of Blaze Currents. 



215 



It is possible to so place the electrode that there shall be no resting 

 current, and this is especially the case in the curarised animal in which 

 the eye-circulation is maintained (Hermann, Holmgren). When the 

 experiment lasted some time the current of rest became reversed,, 

 even when the middle of the cornea was led off from. The response 

 to light is always in the positive direction, i.e., in the same direction 

 as the current of rest. This positive variation is preceded by a 

 negative initial jerk (Vorschlag). When the light is extinguished a- 

 further positive change occurs which subsequently diminishes, at first 

 quickly and then more slowly. Within certain limits the extent of the 

 excursion increases with the duration and strength of the illumination. 

 No negative initial jerk could be observed in the eye of the living frog 

 in response to light • the increase which occurred when the illumination 

 ceased was, however, greater and lasted for a longer time than in the 

 excised eyeball. The return of the needle took place no more quickly 

 than in the excised eye, notwithstanding the maintenance of the circu- 

 lation and the consequent greater activity of assimilation processes. 



Excitation of the eye in the dark by light after previous excitation 

 by electric currents usually resulted in an augmentation of the excur- 

 sion, the excursions actually observed being greater than the sum of 

 the after-effect produced in response to the induction current and the 

 excursion which is the normal response to illumination alone. A still 

 more striking augmentation of the effect occurred after previous faradi- 

 sation (Waller). The fact that the augmentation occasionally eluded 

 observation may be due to the circumstance that the sensitiveness of 

 the galvanometer had often to be reduced by a tenth on account of the 

 largeness of the excursion due to the combined effect of "blaze- 

 currents " and light currents. 



Electrical effects in response to light are given not only by the 

 pars optica retinae, but can be obtained also from the anterior part of 

 the eyeball alone, the excursions, which could only be observed by 

 galvanometer, being, however, very small. The possibility that the 

 heat of the small incandescent lamp which was used for giving the 

 light-stimulus may have been responsible for the effect must be borne 

 in mind, and alterations which may have been produced in the muscles 

 of the iris must also be taken into account. I am at present engaged 

 in making the further experiments that are required with regard to 

 this matter. 



The results obtained with the eyeball in response to excitation by 

 electrical currents are not in any way affected by the absence or 

 presence of light. The currents which occur in the uninjured eye in 

 response to such stimulation are, therefore, independent of the effects 

 produced by light, and are to be sharply distinguished from them, 

 (Waller.) This is confirmed by the following new observation : — 



VOL. LXXI. R 



