150 RESPONSE IN THE LIVING AND NON-LIVING 
vogue and partly also to the differing states of the 
excised eyes observed. 
Waller, in his excellent and detailed work on the 
retinal currents of the frog, has shown how the sign of 
response is reversed in the moribund condition of the eye. 
As to the confusion arising from our present 
terminology, we must remember that the term positive 
or negative is used with regard to a current of reference 
—the so-called current of injury. 
When the two galvanometric contacts are made, one 
with the cut end of the nerve, and the other on the 
uninjured cornea, a current of in- 
jury is found which in the eye is 
from the nerve to the retina. In 

the normal freshly excised eye, 
Fie. 95. Berman Resronse the current of response due fo 
Bigg ies a oa .. the action of light on the retina 
from the nerve to the is always from the nerve, which 
is not directly stimulated by light, 
to the retina, that is, from the less excited to the more 
excited (fig. 95). This current of response flows, then, 
in the same direction as the existing current of reference 
—the current of injury—and may therefore be called 
positive. Unfortunately the current of injury is very 
often apt to change its sign; it then flows through the 
eye from the cornea to the nerve. And now, though 
the current of response due to light may remain 
unchanged in direction, still, owing to the reversal 
of the current of reference, it will appear as negative. 
That is to say, though its absolute direction is the 
same as before, its relative direction is altered. 
