INFLUENCE OF DRUGS ON ELECTRICAL RESPONSE. 535 



this is succeeded by gradual diminution, which is prone to pass into 

 complete abolition with very gradual recovery. These subsequent 

 effects come on even when attempts have been made at cpuite an early 

 stage to remove the vapour from the chamber. A stronger dose of 

 chloroform abolishes the variations, and on removal of the vapour the 

 electrical effect may never reappear, but even when it does it is liable 

 to be permanently diminished in amount. Alcohol vapour causes an 

 augmentation, which persists far longer than in the case of weak ether, 

 and a fortiori than in that of weak chloroform (Fig. 275). The augmenta- 

 tion is seen when the vapour is comparatively strong, and depressant effects 

 are only observed 

 as the result of pro- 

 longed action. A 

 large number of 

 other gases have 

 been investigated in 

 the same way, the 

 details of which 

 cannot be entered 

 into here. There 

 is, however, one gas 

 the action of which 

 is of great physio- 

 logical importance, 

 namely, carbon 

 dioxide. 



Carbon dioxide. 

 — The effects of the 

 passage of C0 2 gas 

 through the cham- 

 ber containing the 

 nerve are as follows. 

 A slight amount 

 causes, during the 

 passage, a primary 

 augmentation fol- 

 lowed by a diminu- 

 tion. These effects 

 are succeeded by a 

 marked secondary 

 increase in the nega- 

 tive variations, 

 which continues for 

 some little time 



after the cessation of the gas, and then gradually subsides. The effects 

 are well displayed in Fig. 274. If the 0O 2 is strong, then the primary 

 augmentation is not observed, and the diminution passes into complete 

 abolition of the electrical effects. The abolition lasts for some little 

 time after the cessation of the CO.,, and is then succeeded by most 

 marked secondary augmentation. 



It will be observed that all the agents above referred to — ether, 

 chloroform, alcohol, and C0 2 — exert both augmentor and depressant 

 effects, possibly related to increased and decreased nerve excitability. 



Fig. 274. — The upper record shows the full effect of "much" 

 carbon dioxide on the negative variation. Temporary 

 abolition followed by secondary augmentation. The lower 

 record shows the effect of little CO., producing secondary 

 augmentation of negative variation. —Waller. 



