I20 



ANIMAL ELECTRICITY 



LECTURE V. 



Instead of a frog's nerve there is now a kitten's 

 nerve upon the two pairs of electrodes p p' e e' (fig. 

 44, p. 102) ; It Is thicker than the frog's nerve, so 

 that our standard deflection by ~^ volt is large, but 

 this is a detail. There Is nothing remarkable about 

 the current of injury. I now test for the negative 

 variation in the usual way, and none is to be seen, al- 

 though the resistance In the exciting as well as in 

 the galvanometer circuit Is small, and although the 



0-5 volt 

 i-o „ 

 1-5 ., 



2-0 „ 



Fig. 50 (2383). — Extrapolar (=" electrotonic ") currents of kitten's nerve, 

 produced by polarising currents of increasing strength from o"5 to 2*0 volts. (The 

 standard deflection by O'ooi volt, not here reproduced, had a value of 40 mm., 

 so that e.£. the A. and K. currents at 2 volts have an E.^NI.F. of about 0*0007 volt.) 



strenofth of excitation be still further increased. This 

 has been no exceptional result ; I have never yet wit- 

 nessed a true action-current from isolated mam- 

 malian nerve, placed upon the electrodes within a 

 few minutes after the death of the animal, whereas 

 frog's nerve under similar conditions has continued 

 to exhibit the action-current for hours and days 

 after excision. The contrast is glaring, and out of 



