RESPONSE OF RETINA TO STIMULUS OF LIGHT 427 



can only be obtained in a tissue of normal high excitability, 

 and not in one which has undergone depression in con- 

 sequence of isolation. I was fortunate enough, however, to 

 meet with a species of fish, Ophiocephalus marulius, whose 

 vitality is so exceptional that it lives for days when taken 

 out of water. When the fish is pithed, its heart continues 

 beating vigorously for many hours. I made a preparation 

 of the eye of this fish and carried out experiments on it 

 under the action of light. 



In fig. 254 is given a record obtained with this specimen 

 during the application of light and on its cessation. It will 



FIG. 253. FIG. 254. FIG. 255. 



FIGS. 253, 254, 255. Parallel Records of Responses given by Plant and 

 Retina, during and after Illumination, illustrative of Type I 

 ( + -f- ). In all these cases up-curve represents induced galvano- 

 metric negativity ; down-curves, positivity. White background in this 

 and following records represent light, and shaded, darkness. 



Fig- 2 53- Response of petiole of Bryophylhim. Light was cut 

 off on attainment of maximum positivity in the second of 

 the multiple responses. 



Fig. 254. Similar effect in response of retina of Ophiocephalus fish. 



Fig. 255. The same with another specimen. Light was here 

 cut off after the first oscillation. 



be seen that during the application of light the sequence was 

 ( I + ). It will be noticed that, after completing two 

 oscillations, and after the response-curve was even slightly 

 reversed at its maximum positive phase the light was with- 

 drawn. The immediate effect was a sudden increase of posi- 

 tivity, followed by a series of after-effect oscillations. In the 

 next figure (255), obtained with a different specimen of the 

 same fish, light was withdrawn at the exact moment of 

 maximum positivity, and the result is seen to be similar to 

 the last namely, an immediate enhancement of positivity, 



