ON ELECTRICAL CHANGES IN MAMMALIAN NERVE. 455 



Eledriccd Changes in Mammalian Nerue. — Report of the Committee, 

 consisting of Professor F. Gotch (Chairman), Professor E. H. 

 Starling, Dr. J. S, Macdonald (Secretanj). (Braion up hij the 

 Secretary.) 



The experiments performed witli the assistance of grant from the Asso- 

 ciation have been directed towards the acquisition of information as to 

 the effect upon the demarcation current of mammalian nerve of 

 alterations in resistance, such as are found in mammalian nerve accom- 

 panying changes of volume and of blood-pi-essure in the vessels supplying 

 the nerve. The nature of the changes of resistance is easilj' determined 

 but the effect of such a change in presumably causing not only an altera 

 tion in the magnitude, but also in the distribution of current and dif- 

 ferences of potential in the nerve, is not easy to calculate. 



Not only this, but it is impossible even to decide the direction of 

 change (addition or subtraction) in the demarcation current which would 

 be produced by any alteration of the internal resistance of the nerve. 



Knowledge of an exact character is required for this purpose, defining 

 the limits of the demarcation source and the extent to which the source is 

 short-circuited in the tissues of the nerve itself. It was felt that such 

 knowledge must be based entirely upon experiments upon nerve, and as 

 far as possible upon the particular nerve for which the information was 

 desired. 



With this object a large number of experiments have been performed 

 upon excised mammalian nerve. The nerves after removal were placed 

 upon a number of non-polarisable electrodes (four to seven), the potential 

 differences between each pair of electrodes determined, as also the resist- 

 ances of the whole nerve and the sections into which it was divided by 

 the electrodes. The electrode upon which the cross-section lay was then 

 permanently connected by a wire or through a known resistance to one of 

 the other electrodes, and the differences of potential between each possible 

 Dair of electrodes determined again after the formation of this circuit. 



An analysis of the data gained by determination of the various resist- 

 ances divides the facts of experiments into the following groups : — 



(rt) The resistance per centimetre determined from the measurement 

 of resistance of any given length of the nerve varies with that length, 

 being smaller for the greater length. 



(b) The resistance of the whole nerve directly determined is a smaller 

 value than its resistance calculated from a summation of the resistances 

 of the several sections between pairs of electrodes. 



(c) The resistance of that section of the nerve bounded by the cross- 

 section gives a smaller value for the resistance per centimetre of the nerve 

 than any other section. 



An observation of these facts has led to a routine method for calcu- 

 lating the resistance of any short length of nerve when the resistance 

 required is not that to a current entering and,leaving at the extremities 

 of the short length, but the gross longitudinal resistance to a current 

 travelling in paths parallel to the long axis of the nerve. The resistance 

 obtp,ined from the longest available stretch of nerve provided with a cross- 



