92 ANIMAL ELECTRICITY. LECTURE IV. 



possible seat of this effect, which may obviously arise 

 at many sorts of interfaces between the various tissues 

 traversed by the current, but give the experiment as it 

 stands, in evidence of an internal polarisability of living- 

 tissues taken en bloc. Obviously it gives no specific 

 information as regards the polarisability of any one 

 particular tissue. 



The second of our two stepping-stones towards 

 the case of nerve is a purely physical experiment — 

 indirectly demonstrative of a peculiar distribution of 



i 



ULOJUt 



4 .3-.^-*/ A— 'K 



Fig. 39. — " Anelectrotonic " current from a core-model. 



current, effected by polarisation, and characteristic of 

 nerve, which is just the one tissue among all other 

 tissues in which polarisation is most easily produced, 

 yet most difficult to directly demonstrate by reason of 

 its extreme evanescence. I know of no direct means 

 by which to demonstrate an internal polarisation of 

 living nerve. The chief evidence of polarisation is in 

 fact the peculiar extrapolar distribution of current 

 along a nerve, termed an electrotonic current, and it is 

 a similar extrapolar current that we are about to wit- 

 ness upon a polarisable core-model consisting of a 

 platinum wire surrounded by a fiuid sheath of zinc 

 sulphate. 



