1 5 o 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, 

 FIG. 95. KETINAL RESPONSE the current of response due to 



TO LIGHT ^ act j on Q f y ^ OE[ ^ ret j na 



The current of response is 



from the nerve to the j s always from the nerve, which 



retina. J 



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. 



