IX ELECTRICAL EXCITATION OF NERVE 195 



Pfliiger's law can also be demonstrated on secretory nerves^ 

 the o-alvanic alterations in "land-cells be taken as the index of 



O " 



excitation. This is easily shown on the frog's tongue if the 

 glosso-pharyngeal nerve is excited (Biedermann, 8). Here again 

 we see that constant currents are much more appropriate for the 

 excitation of secretory nerves than single induction shocks, which 

 with even powerful intensities produce hardly any modification of 

 the lingual current, while the single closure of a medium battery 

 current invariably produces visible consequences. This striking 

 disparity of action is undoubtedly, in either case, caused solely by 

 dissimilar duration of the currents thus not merely testifying 

 against the infallibility of du Bois' " universal law of excitation," 

 but proving the accuracy of the view of Griitzner and Schott, 

 viz. that rapid stimuli excite the quickly reacting, slow stimuli 

 the more sluggish end-organs. If, with a strong ingoing lingual 

 current, 36 Dan. are closed in the descending direction, after 

 previous compensation of the current, there will regularly be- 

 after a short latent period (12 sec.) a monophasic negative 

 variation, which is often of considerable strength, persisting for 

 some time during closure, and vanishing rapidly when the circuit 

 is broken ; whereupon, if the current is not too strong, the break 

 excitation appears as a delay, or even as a brief arrest of the 

 backward impulse. This is usually still more plain on exciting 

 with ascending currents, closure of which produces the same 

 monophasic, albeit essentially weaker, negative variation as the 

 descending direction. If very strong currents are employed, the 

 effects may correspond throughout with the third stage of the " law 

 of contraction " ; since with the descending direction a " closure 

 variation," with the ascending direction an " opening variation," 

 alone appears. As we should anticipate, the alternate closure of 

 opposite currents by means of a Pohl's reverser invariably 

 results in an excessively strong variation of the current of rest. 



Pflliger (46) was again the first to investigate the action of 

 currents of different direction and intensity upon centripetal 

 (sensory) nerves, using the reflexes discharged as indications of 

 excitation. The frogs were weakly strychninised, and current 

 then led through the isolated sciatic the unskinned leg remain- 

 ing attached to the nerve, to avoid artificial cross-sections. The 

 presumptions of Marianini and Matteucci for strong currents 

 were entirely realised. Reflexes were excited only by closure 



