328 



On the Eetinal Currents of the Frogs Eye. 



4. The magnitude of the response to light increases with the 

 strength of illumination. 



5. With lapse of time — or immediately in consequence of partial 

 injury, the character of the response to light alters its type. Three 

 stages are to be recognised in accordance with the state of the 

 retina, as (a) fresh ; (h) transitional ; (c) stale. 



In the first stage the response is positive. 

 In the second stage the response is mixed. 

 In the third stage the response is negative.* 



Theory. — Simultaneous opposite electrical effects are aroused in the 

 retina by light. 



6. The interval of time between stimulus and response is much in 

 excess of a physiological latent period. In the second stage this- 

 " period of hesitation " may amount to five seconds. 



Fia. 3. 



Seconds i I5 ' ' ' ' /^o ^fe 2^ 



I 



7. Under the influence of carbonic acid the response to light under- 

 goes diminution or abolition followed by secondary augmentation. 



8. In consequence of tetanisation in either direction the normal 

 current becomes strongly positive (or less negative). This positive 

 change gradually subsides. 



9. The positive response to light subsequent to such tetanisation 

 is much augmented, and the negative response is diminished. 



* I have made a few experiments on mammalian eyes (eat), justifying tlie^ 

 statement that the response immediately after removal is positive, and that at ai 

 later period it is negative. 



