JO ANIMAL ELFXTRICITV.^ — LECTURE IIL 



evolved nerve. Such nerve consists of proteld axis 

 and fatty sheath ; the axis — which is the offshoot of a 

 nerve-cell — is the specially conductile part, the sheath 

 is a developmental appendix, not directly connected 

 with any nerve-cell. Yet, cut the nerve, and sheath 

 as well as axis undergo Wallerian degeneration, 

 which is evident proof of a functional commerce 

 between sheath and axis. You have seen further, 

 that such nerve is inexhaustible, yet that it exhibits 

 very clear symptoms of chemical change after action. 

 All these things, to my mind, reconcile themselves 

 with the notion that the active grey axis both lays 

 down and uses up its own fatty sheath, and that it is 

 inexhaustible, not because there is little or no expendi- 

 ture, but because there is an ample re-supply. 



This is wild hypothesis — an unbridled excess of 

 the imagination — and I shall be the first to admit 

 this, nor claim for it any value other than as a possible 

 motive for further trial. 



Still, leaving aside the imaginary reinvolution of 

 CO2 and the imaginary origin of specially conductile 

 strands, let me at least urge that the staircase effect as 

 a general phenomenon gains value in a definite and 

 concrete sense, both as a physiological and as a psycho- 

 logical idea, when we have admitted that carbonic acid 

 is a product of nerve activity and that carbonic acid 

 facilitates nerve activity. From a physiological stand- 

 point it seems to me preferable to admit as an effective 

 factor of ''summation " and of " staircase effect " and 



