General plan of apparatus employed to investigate the influence of 

 reagents upon the electrical response of isolated nerve. 



The iierveeliaiiiher cmita 

 cirodes connected wiih K,, 



IS I lie nerve resiing upon a pair of iiiipolarisahle 

 . ;iri>l a pair of platinum elcctioiles, through which 

 the nerve is excited. The w.ashliollle serves to prevent drying of the nerve, an.l 

 in certain cases is used to slop acid vapour. 



'K\\e exciling apl>aratiis is represented above; the circular interrupter in the 

 primary circuit revolves once a minute, and makes contact at a mercury pool for 

 ; of each revolution. The vibrating interrupter of the coil starts as the circuit is 

 completed, an<l the nerve is thus letanised each minute for 7J seconds, at a fre- 

 ipiency of 70-75 interruptions per second. 



The keyboard is composed of four bridging keys : K, in connection with the 

 nerve at T and L, !-:„ with the compensator, K, with the recording galvanometer, 

 and K, on occasion with a demonstrating galvanometer. When all the keys are 

 closeil everything is short-circuited through Ihem ; the keyboard is then simply 

 a metallic ring. Opening K, and K, puts the nerve into connection with the 

 galvanometer : opening K, lets into the nerve-circuit any suitable fraction of a 

 volt from the cell and rheostats r R. To take 0001 volt from a Leclanche 

 cell, r is taken - 10 ohms, and R ^ 14,690 ohms : to take a polarisation current 

 ol o-oi voir, r is inken - too ohms, and R 14,600 .ihms, Xr. 



N.B.-The galvanometer records its movements to Right and Left of 

 some arbitrary position of rest. The connections and disposition of the 

 apparatus are such that deflections to the Right or Northwards represent 

 positive effects, and deflections to the Left or Southwards represent 

 negative eff^ects. 



The completed records (with the exception of Figs. 42 and 43) are 

 turned so that positive deflections to the Right or North read upwards, 

 and negative deflections to the Left or South read downwards. 



Thus ;/. the negative variation reads downwards, anodic deflections 

 read upwards, kathodic effects read downwards. 



