218 



Dr. A. Durig, A Contribution to 



[Nov. 20, 



inner surface of the removed cornea was placed on a little projection 

 of the kaolin of the one electrode, the outer surface was connected by 

 a thick piece of wick with the other. In response to every stimulation, 

 large " blaze currents " occurred, which in all respects resembled 

 those of the whole eyeball, even in their intensity, so that one would 

 not have known that the experiment was not being made with the 

 whole eye unless one had seen the preparation. The resting current 

 was from the inner to the outer surface; each induction shock, in 

 whichever direction, produced an effect in the same direction as the 

 resting current. When the excitation was also in the same direction 

 as the resting current, this (outgoing, Transl.) response was pre- 

 ceded by a well-marked initial effect in the opposite direction. 



According to these observations, the principal place in which the 

 "blaze currents" of the eyeball originate appears to be the cornea, 

 while the ciliary ring and lens contribute thereto. The retina plays 

 quite a subsidiary part in their production. The results of these 

 experiments on the cornea give support to the analogies between 

 skin and cornea in their behaviour to excitation, to which Waller, by 

 comparing the eyeball and skin currents, has already drawn attention,, 

 although it must not be forgotten that, owing to the difficulty in pre- 

 paring it, the cornea is a much damaged tissue. 



The fact that the cornea, an epithelium which is free from mucous 

 cells, possesses strong electromotive properties, has a distinct bearing 

 on one question which has been sometimes discussed, namely, that as 

 to whether it is the mucous cells or the ordinary epithelial cells that 

 are the cause of the occurrence of differences of potential in skin, 

 tongue, &c. 



There is another point of interest in connection with these experi- 

 ments which may be here mentioned, which is, that the "blaze 

 currents," after reaching their maximum, seldom diminish at a 

 constant rate. The diminution frequently takes place in a series of 

 steps, i.e., the current, after beginning to diminish at a regular rate, 

 suddenly ceases to diminish for a few seconds or is even slightly 

 augmented, thus causing a projection on the curve ; it then diminishes 

 again at its previous rate, being interrupted at intervals by fresh 

 augmentations. This phenomenon also requires further study. In 

 order not to increase the length of this communication, the curves 

 obtained and the numbers from which they were derived will not be 

 introduced. 



It is the retina especially from which one might have expected to get 

 large electromotive effects. The fact that the response to excitation 

 observed in it was so small (and the little there was may not even have 

 been entirely due to the retina, since the optic nerve and the sclerotic 

 remained attached) is enough to suggest the question whether "blaze 

 currents " may really be taken as a sign of the persistence of life, 



