1903.] Phenomena in Mammalian Non-medullated Nerve. 179 



3 



i 



4 



4-8 



\ 



j 



I 



A: 







J A. 





230. 







"VIII. 



K 



6 volts. 



•001V. 



fl 



Fig. 10. — Exp. 730, VIII. A. and K. Currents only, with Increasing Strength? 

 of Polarising Currents. 



in A and ■ 595 millivolt in K in Experiment 728), in the splenic nerves- 

 the anelectrotonic currents are perhaps four times greater than the 

 katelectrotonic. This favours the view that these currents are not due 

 to the presence of a small percentage of medullated fibres in these- 

 nerves, but are the actual expression of the fine sheaths present around 

 the axis-cylinder.* 



The result, therefore, of this series of experiments affords a very- 

 probable explanation of the diminution of the negative variation with 

 successive excitations in the non-medullated nerve, and the relative- 

 absence of this diminution in the medullated. For in the latter the 

 exciting current can diffuse up and down the nerve, in the former it i& 

 strictly limited to the spot where it is applied, and the current density 

 at the excitable axis-cylinder must be many times greater in the non- 

 medullated nerve. It is not surprising, therefore, that there should be- 

 a marked local effect, and whether this is termed " injury" or "-fatigue " 

 is rather a question of terminology than of fact. 



* Dr. W. M. Fletcher has recently examined the sheaths of medullated and 

 non-medullated fibres between crossed nicols. He finds that in the former there- 

 is characteristically present an anisotropic cholesterin deposit ; in the latter this is 

 absent. The sheath round the non-medullated axis-cylinder is therefore of a 

 totally different character to that in the medullated fibre. (Note communicated to 

 the writer.) See also authors quoted by Brodie and Halliburton, lac. cit. 



