The Demarcation Current of Mammalian Nerve. 315 



phenomena, one a function of the condition of life of the nerve and the other 

 a physical phenomenon dominated by the salt content of the nerve, and capable 

 of continuation long after its death. 



***** 



6. If a number of threads are twisted together to form a rope and 

 the rope laid upon two non-polarisable electrodes of the usual type, no 

 current is found between the electrodes if the thread rope is previously 

 uniformly wetted with a saline solution or with tap water. If on 

 such an uniformly wetted rope a drop of saline solution of a different 

 concentration is placed at a point closer to one electrode than another 

 a current is found in the circuit, and a source of E.M.F. quite com- 

 parable in value to the maximal value of the demarcation source of 

 a nerve. A drop of the same solution placed upon a corresponding 

 point of the rope nearer to the other electrode may reduce, bring to 

 zero, or reverse this difference of potential. 



This phenomenon is presumably due to the upsetting of the balance 

 between the osmotic processes taking place in the two non-polarisable 

 and " similar " electrodes. 



***** 



7. The close association of the value of the demarcation current 

 with the salt content of the nerve suggests a similarity between the 

 experimental phenomena observed in the thread and in the nerve, and 

 the causation of the demarcation current of nerve as due to a balance 

 between two unequal osmotic processes, one at the cross section and 

 one at the longitudinal surface. 



***** 



The expenses of this research have been partially defrayed by a 

 grant from the British Association. 





" The Demarcation Current of Mammalian Nerve. (Preliminary 

 Communication.) II. The Source of the Demarcation Cur- 

 rent considered as a Concentration Cell." By J. S. MAC- 

 DONALD, B.A., L.R.C.P.E., University College, Liverpool, 

 Research Scholar of the British Medical Association. Com- 

 municated by Professor SHERRIXGTON, F.R.S. Received 

 September 25, 1900. 



The changes produced by the action of tap water upon the nerve 

 have, in the interval, been more closely studied. Excluding alterations 

 of E.M.F., they are as follows : 



