NER VE. 



either an anode or a cathode, the polar region thus constituted is 

 surrounded on all sides by what may be termed a peripolar region of 

 opposite sign. The conditions are such that in the polar region of the 

 actual electrode the current density will be most marked, whilst in the 

 peripolar region it will be far less. With gradually increasing intensities 

 of current, the muscular response to stimulation over the entry of the 

 nerve must vary in consequence of these conditions. This is show r n by 

 the results given in the following table : l 



A portion of the peripolar region is obviously on the myopolar side 

 of the polar, and thus may cause conductivity changes when the 

 current is sufficiently intense. 



This and the great difference between the denser polar and diffuse 

 peripolar regions readily explains the occurrence of the responses, which 

 are therefore really in accordance with Pflliger's law as determined in 

 isolated nerve. Two interesting features come into special prominence 

 by the use of this method upon man. First, the prolonged response on 

 the closure of strong currents with cathode upon surface ; secondly, the 

 marked increase in the period of delay in the muscular response to the 

 opening polar anodic excitation. This was found by Waller to amount 

 to 0*03 sec. It appears that the delay is associated with impairment 

 in conductivity from which the nerve does not recover until O03 sec. 

 after the current has ceased to flow. 2 Although, therefore, the excita- 

 tion occurs at the moment of opening, the impairment of conductivity 

 persists and delays the propagation of the excitatory state. 



In these respects the results confirm those obtained on isolated 

 nerve, though in man they are modified by the diffuse peripolar and 

 intense polar condition previously referred to. 



Polar excitation of peripheral sensory organs. Taste organs. If 

 a current traverses the tongue in man, an acid taste is localised at 

 the contact when the anode is on the tongue, an alkaline or salt taste 

 when the cathode is placed there. The sensations last during the whole 

 time of closure, are reversed on the cessation of the current, and can 

 be obtained with unpolarisable electrodes. 3 The susceptibility of the 

 taste organs to such excitation is extremely delicate. The acid anodic 



1 Waller and de Watteville, Phil. Trans., London, 1882 ; Proc. Roy. Soc. London, 1882. 



2 Waller, Arch, dephysiol. norm, etpath., Paris, 1882, p. 383. 



3 Rosenthal, Arch. f. Anat., PhysioL u. wissensch. Med., 1860; Biol. CcntralbL, 

 Bd. vi. S. 120. 



