230 



SPECIAL PHYSIOLOGY. 



But according to Pfliiger and Heidenhain the results are modified by 

 the strength of the currents employed, as expressed in the following 

 table : 



Valentin maintains that, with moderate currents, contraction occurs 

 only at the closure, or commencement, of the current, whether this be 

 direct or inverse ; any other results, he refers to the effects of injury 

 to the nerve. With stronger currents, contractions occur at both the 

 commencement and the end, the latter being the weaker. As regards 

 very strong currents, Valentin's observations coincide with Pfliiger's. 

 Budge, however, has found that very strong currents produce con- 

 traction, both at the moment of closure and opening, whether they be 

 direct or inverse. The different results arrived at by equally careful 

 observers, indicate the necessity for yet further investigations in this 

 difficult subject. 



It has been shown that the muscular contractions are more intense, 

 the further from the muscle, i. e., the nearer to the nervous centre, 

 the stimulus is applied; this proves either that the nerve is more irri- 

 table near its centre of origin, or that the energy of a nerve increases 

 as it is propagated onward (Pfliiger and Budge). The latter view is 

 adopted by Pfluger. 



The electromotive properties, or electrical currents, of sensory 

 nerves, are precisely identical with those of the motor nerves, and so 

 likewise they present identical electrotonic phenomena ; hence an argu- 

 ment is derived in favor of the opinion, that both kinds of nerve fibres 

 may conduct impressions in each direction. But the physiological 

 reactions of the sensory nerves are somewhat different. Thus, in 

 their case, the strength of the current influences the results ; a continu- 

 ous current causes continuous excitement, instead of interfering with 



