III. 



TETANISATION AND ILLUMINATION 



55 



response to light by strong tetanisation, and vice versa for modi- 

 fications of the response to induction shocks by strong illumina- 

 tion, I also took series of positive responses to light and to 

 weak tetanisation alternated, to see whether or no they would 

 decline pari passu. An example of such a series has been 



voit 



00/0 



0005 



\ 



FlG. 24. Frog's eyeball. Series of normal responses to light and to tetanisation 

 alternated ; each excitation lasts for one minute. The response to tetanisation falls 

 more rapidly than that to light. 



figured above. The series of responses to tetanisation appears 

 to decline more obviously than does the series of responses to 

 light. But the difference is not very striking, and in other 

 records it is even less so. In fact, when I took the records, I 

 thought they justified me in saying that the two kinds of response 

 wear out in a parallel manner. Clearly, however, the parallelism 

 has not always if ever been absolute ; the instance figured above 

 exhibits more rapid decline of the tetanisation responses than 

 of the light responses. The point clearly needs to be tested 

 again. As regards modification of the response to induction 

 shocks by strong illumination, we have seen that no appreciable 

 effect occurs. As regards modification of the response to light 

 by strong tetanisation, we have seen that the regular effect has 

 been an increased response during and after tetanisation. Indeed, 

 the resistance of the retina as regards its excitability by light 

 has been a constant yet surprising feature. The strongest tetani- 

 sation at my disposal (Berne coil, 2 Leclanches, secondary over 

 primary coil, current unbearable by wetted fingers) has failed 

 to abolish its response to light. And strong tetanisation (10,000 

 units) that has completely abolished all blaze-reaction (as e.g., 



