98 ANIMAL ELECTRICITY. LECTURE IV. 



extrapolar effects are well-marked and of equal 

 mag-nitude. They are completely abolished by 

 pinching the nerve between the two pairs of 

 electrodes. 



These last experiments — that relating to frog's 

 nerve in particular— will form the point of departure 

 of my next lecture. We shall then become fully 

 convinced of the "physiological" nature of these 

 extrapolar currents — at least in the case of frog's 

 nerve. Of mammalian nerve I have little know- 

 ledge, and therefore, little to say. Isolated mam- 

 malian nerve gives no " negative variation," and I 

 was thereby deterred from taking It as an object of 

 systematic study. At present it is to me a rather 

 mysterious stranger. 



hote. — Electrotonic currents, according to Biedermann, 

 are much less marked on non-medullated than on medullated 

 nerves, the katelectrotonic current in particular being absent. 

 This however is denied by Boruttau (Pfliiger's Arcliiv, Ixvi., 

 p. 285, 1897). 



The presence of electrotonic currents on non-niedullated 

 nerves is in apparent contradiction with the view taken in 

 these lectures, that the interface between grey axis and fattv 

 sheath is the surface at which electrolytic polarisation takes 

 place. But the non-medullated state is not absolute, many 

 non-medullated nerves are more or less distinctly and 

 continuously myelinated, and in any case electrotonic 

 diffusion appears to be much less pronounced than on fully 

 myelinated nerves. There may prove to be some signili- 

 cance in the relation that apparently obtains in the com- 



