III.] 



BLAZE-CURRENTS 



47 



such ; I characterise it, in distinction from the next variety of 

 current that you will witness, as equivocal or antidrome. The 

 current is subsiding, rapidly at first, now more gradually, and 

 more and more so as the spot approaches its zero position, some- 

 times, indeed, we may witness a permanent positive deflection, a 

 current-remainder reminding one of the contraction-remainder 

 of muscle. 



I will now test the eyeball by an induction current in the 



VoLb 



J_ 



mms. IO 



/? - zooo 



o mins. 



10 



20 



FlG. 21. Normal blaze-currents of a frog's eyeball in response to excitation by 

 a single break induction current in the negative or antidrome direction (B - 2000), 

 and in the positive or homodrome direction (B + aooo). 



positive direction ; so I adjust the compensation and turn a 

 reverser in the induction circuit, send a break induction shock 

 through the eyeball in the positive direction, and unplug the 

 galvanometer. The spot flies off to your right as before. That 

 also has been a blaze-current, of positive direction in response to 

 an induction shock of positive direction ; it is evidently not a 

 polarisation current ; I characterise it in distinction from the 

 first variety as unequivocal or homodrome. 



This, in my opinion, is a cardinal experiment, and when it 

 was deciphered, became sign-post as well as hinge of further and 

 more general investigation. 



But let us complete the experiment. The eyeball upon 

 which you saw a moment ago that two very large responses in 

 one and the same direction followed excitation by single break 

 shocks first in one and then in the opposite direction has been 

 plunged into hot water, i.e., killed and replaced between the 

 electrodes. I repeat the test of a right and left induction shock 

 and no movement whatever of the galvanometer spot is to be 

 detected. The dead eyeball gives no blaze-current. 



