176 



Dr. N. H. Alcock. The Electromotive 



[Dec. 15, 



recorded above, may possibly be explained by supposing that the 

 splenic c ontractions are not as delicate an index of the condition of 

 the splenic nerves as the galvanometric response. Waller* has shown 

 that with a gradually increasing stimulus the voltage of the negative 

 variation reaches its maximum much later than the contraction of the 

 attached muscle, and as in all the experiments here recorded a certain 

 amount of the negative variation still persisted, it is possible that even 

 this fraction — perhaps one-third of the initial value — indicated a 

 sufficient intensity of nerve impulse to give a maximal splenic 

 contraction. 



If the medullary sheath has any such action as the hypothesis 

 suggested above necessitates, the inquiry may be extended to see if 

 any light can be thrown on the manner in which this sheath acts. 

 The following experiments on electrotonic currents were, therefore, 

 undertaken. 



2. Electrotonic Currents. 

 Methods. 



The nerve rested upon two pairs of non-polarisable electrodes. 

 The distal pair led off to the galvanometer ; the proximal were con- 

 nected with the automatic reverser, used by Dr. Waller in 1897, which 

 delivered in order — 



(1) A current in the proximal direction (giving anelectrotonic 

 currents in the nerve). 



(2) Excitation by means of an induction coil. 



(3) A current in the distal direction (katelectrotonic currents). 



(4) Excitation as No. 2. 



The result is seen in the photographic plate as a cycle consisting 

 of one upward mark, anelectrotonus, and three downward, the middle 

 one katelectrotonus, the two side negative variations. 



Experiments. 



The following pair of experiments was made under identical 

 conditions : — 



Table VI. 



Experiment. 



Nerve. 



Anelectro- 

 tonus 

 mean. 



Neg. var. 

 mean. 



Katelectro. 

 mean. 



Inj. cur. 



Notes. 



728 VIII . . 



Median 



-702 



0-356 



0-595 



0-20 



Fig. 8 





(branch of) 











729 A YIII 



Splenic 







0-540 







0-80 



Fig. 9 



* Waller, 4 Brain,' vol. 18, 1895, p. 210. 



