INORGANIC RESPONSE 151 
I have already advocated the use of the term 
positive for currents which flow towards the stimulated, 
and negative for those whose flow is away from the 
stimulated. If such a convention be adopted, no con- 
fusion can arise, even when, as in the given cases, the 
currents of injury undergo a change of direction. 
Normal response positive —The normal effect of light 
on the retina, as noticed by all the observers already 
mentioned, is a positive variation, during exposure to 
light of not too long duration. Cessation of light is 
followed by recovery. On these points there is general 
agreement amongst investigators. Deviations are re- 
garded as due to abnormal conditions of the eye, owing 
to rough usage, or to the rapid approach of death. 
For just as in the dying plant we found occasional 
reversals from negative to positive response, so in the 
dying retina the response may undergo changes from 
the normal positive to negative. 
The sign of response, as we haye already seen in 
numerous cases, depends very much on the molecular 
condition of the sensitive substance, and if this condi- 
tion be in any way changed, it is not surprising that the 
character of the response should also undergo alteration. 
Unlike muscle in this, successive retinal responses 
exhibit little change, for, generally speaking, fatigue is 
very slight, the retina recovering quickly even under 
strong light if the exposure be not too long. In 
exceptional cases, however, fatigue, or its converse, the 
staircase effect, may be observed. 
Inorganic response under the stimulus of light.— 
It may now be asked whether such a complex vital 
