INORGANIC RESPONSE  t6F7 
‘When diffuse light is allowed to impinge on the eye of 
the frog, after it has arrived at a tolerably stable 
condition, the natural E.M.F. is in the first place 
increased, then diminished ; during the continuance of 
light it is still slowly diminished to a poimt where it 
remains tolerably constant, and on the removal of light 
there is a sudden increase of the E.M. power nearly ap 
to its original position.’ ! 
(3) I have sometimes obtained the following curious 
result. On the incidence of light there is a response, 
say, upward. On the continuation of ight the response 
declines to zero and remains at the zero position, there 
being no further action during the continuation of 
stimulus. But on the cessation or ‘ break’ of light 
stimulus, there is a response downwards, followed by 
the usual recovery. This reminds us of a somewhat 
similar responsive action produced by constant electric 
current on the muscle. At the moment of ‘make’ 
there is a responsive twitch, but afterwards the muscle 
remains quiescent during the passage of the current, but 
on breaking the current there is seen a second respon- 
sive twitch. 
Résumé.—So we see that the response of the 
sensitive inorganic cell, to the stimulus of light, is in 
every way similar to that of the retina. In both we have, 
under normal conditions, a positive variation; in both 
the intensity of response up to a certain limit increases 
with the duration of illumination ; it is affected, in both 
alike, by temperature; in both there is comparatively 
little fatigue ; the increase of response with intensity of 
' Proc, Roy. Soc. Edin. 1873, p. 153. 
