496 SCIENCE PROGRESS 



from which the fibres do not recover, there is then present at 

 such cross-sections a stationary excitation. Now we have 

 shown that the transference of excitation is a matter definitely 

 to be set on one side as due to an electrical agency — that is 

 to say to a motion of electrolytes. Since we must think of this 

 motion of electrolytes as produced by an alteration of the 

 character or quantity of electrolytes present at an excited point, 

 we may expect to find at a fatally excited point the new or 

 additional electrolytes thus known to be characteristic of this 

 state. 



There is no evidence that the nature of the electrolytes is 

 new. Here we are down upon an old bone of contention. It 

 has been suspected that a decomposition process occurred 

 at such injured points attended with an output of carbonic 

 acid and waste products of a similar kind. There is, however, 

 no acidity to be detected. If there were, the amount necessary 

 to account for the phenomenon would have to rise to a value 

 instantly detectable. This is shown by the fact that this 

 injury current, which may be modified by alkali as by any other 

 electrolyte, is not annihilated by a value of caustic soda solution 

 below 0*8 per cent., and that solutions of hydrochloric acid 

 may equally well be used for this annihilation. Place this 

 beside the fact that it is possible to identify the additional 

 potassium evoked by the injury by microchemical means, and 

 it seems certain that injury produces not an electrolyte of a 

 new character but an additional quantity of such electrolytes as 

 were already present. A study of the injury current therefore 

 may be taken to have revealed the existence of a solution of 

 extraordinary concentration in the excited region of the nerve- 

 fibre. It seems obvious that excitation may modify the strength 

 of the solution present in one of two ways — either by withdrawal 

 of water for combination with some more solid material not 

 to be reckoned as part of the " solution," e.g. in a solid phase, 

 or by release of potassium salt from under cover of some 

 such solid phase into the quantity of material to which the 

 general character of "aqueous solution" is due, or from some 

 state of chemical combination. 



The terms in which the last sentence are couched are the 

 result of a microscopical study of the core of the nerve-fibre. It 

 is impossible long to pursue a study of nerve-fibre structure 

 without being impressed by the colloidal character of the 



