284 On the Injury Current in Mammalian Nerve. [Dec. 10, 



mammalian body. Cooling must, therefore, continue after the nerve has 

 reached the electrodes • and this cooling is not a perf ectly simple matter, 

 for the fatty sheath of the nerve is not only, probably, a bad conductor of 

 electricity, but also undoubtedly an indifferent conductor of heat, 

 we should expect, therefore, the cooling process to be differential, 

 the temperature of the external solution falling sooner than that 

 of the internal solution or axis cylinder • and since cooling is 

 in a manner equivalent to dilution, the concentration ratio of the 

 two solutions should be at first increased, and with it the value 

 of the E.M.F. 



The theory then affords an explanation of the increase observed 

 when a nerve just out of the body is examined at a lower tempera- 

 ture. It remained to further exemplify this fact by attempting to 

 reproduce the phenomenon at will. An experiment was so arranged 

 that the proper temperature of the nerve was artificially maintained, 

 and then at a given moment allowed to fall gradually. The resulting 

 curve shows that at or near body temperature the injury current 

 declined rapidty ; in this particular case it fell in half-an-hour 44 per 

 cent, of its original value. In the second portion of the record 

 during the period of cooling, the rapid fall was arrested, there was a 

 period of hesitation, and then a slow rise of the current. On the 

 temperature being again raised, the current resumed its rapid decline. 

 In such an experiment the alteration of condition obtained by fall of 

 temperature is comparable to that produced by dilution of the 

 external solution, and the results are in complete agreement. 



It is not surprising that to obtain such an initial rise it is necessary 

 to restrain the fall of temperature within certain limits, outside of which the 

 effect is masked by a more powerful factor working in the direc- 

 tion of diminution. Where, for example, a nerve fresh from the 

 body is transferred to a temperature of 0' C, there is no initial 

 increase ; for here the difference of temperature between nerve and 

 surroundings being great, the rate of cooling will be rapid, and 

 internal solution as well as external will be quickly affected, 

 and to cool the internal solution is equivalent to diminishing its con- 

 centration and hence to a lowering in value of the diffusion process. 



Extreme cooling should, indeed, annul the production of the injury 

 current, by arresting the processes of diffusion upon which its mani- 

 festation depends. Yet, in a cooled nerve, the source of the pheno- 

 mena, the concentration ratio, is preserved, and a raising of the tem- 

 perature ought again to develop the injury current. This expectation 

 is fulfilled experimentally. At a temperature near 0° C. the current 

 declined rapidly, but it regained its value to a great extent as the tem- 

 perature was increased. With a nerve maintained at body tempera- 

 ture the injury current fell rapidly. A high temperature favours 

 diffusion (i.e., the equalising of the solutions), and the phenomenon 



