278 SOME CHAPTERS ON THE 



tions that a nerve fibre has a structure consisting of a " core " 

 containing a concentrated solution of electrolytes, a semi-permeable 

 membrane outside this, and outside the membrane a " sheath " 

 containing dilute electrolytes. 



(4) From the concentration law E w = E a x leg - a calculation 

 can be made of the concentration of electrolytes in the core. For 

 when w=l, then as log 1 = 0, = (), therefore a solution of ~ 



(dissociated) MCI would cause the injury current to vanish, and 

 would presumably be equal in E.M.F. to the solution of the 

 electrolytes in the axis cylinder. If these consist of KC1, this 

 concentration is nearly 10 per cent. 



(5) The conductivity of this solution in the axis cylinder can 

 also be calculated, if this conductivity of the whole nerve is known, 

 if the relative amounts of axis cylinder, sheath, and connection 

 tissue are estimated, and if the conductivity of the sheath be 

 supposed to be the same as that of the solution in which the nerve 

 is placed for a short time. Macdonald gives the value from these 

 data as equal to 2'5 per cent. KC1 very approximately. 1 



(6) Under the microscope the axis cylinder of a living tissue 

 is clear and transparent. 2 At the injured end granules are seen, 

 and these stain with neutral red. These red-stained granules 

 gradually appear further and further down the nerve, and the 

 rate of appearance varies as the concentration of the fluid bathing 



the fibres, being '17 x 10~ 5 cm. per second for ^ NaCl, -30 x 10~ ; 

 for ^ NaCl. Macdonald infers that this process gives a graphic 



representation of the diffusion of the ions causing the injury 

 current. Toluidine blue gives a rather different appearance which 

 may represent the action current. 



(7) Macdonald agrees with Macallum in his picture of the 

 distribution of chlorides in the axis cylinder, but disagrees as to 

 the distribution of potassium. He declares that while potassium 



1 Some unpublished experiments indicate that this value may require revision. 

 The strength of solution in which the sciatic nerves of the cat remain unaltered in 

 weight is 1-16 per cent. NaCl ( 80 ). 



* All authors agree with this. If the fibre is fixed different appearances are 

 seen ; that usually accepted as the best shows longitudinal fibrils in. a clear or 

 granular matrix. Ashworth ( 41 ), examining the giant nerve cells and fibres of Halla 

 parthenopeia, where these appearances are very distinct, finds quite definite fibrils, 

 arising from the nerve cell and continued into the nerve fibre. If the nerves in 

 the animal resemble those in the frog, this observation supports the usual vit-\\. 



