216 PHYSIOLOGY CHAP. 



On experimenting with a bundle of six frogs' sciatics, cooled 

 to 5 C. in order to delay the transmission of the wave of the 

 current of action, Hermann, with the rheotome, succeeded in show- 

 ing its diphasic character, i.e. the negative phase is followed by a 

 positive phase which is different in form, but of the same algebraic 

 value (Fig. 141). This was confirmed by Boruttau for the non- 

 medullated nerves of Octopus and Eledone, in which the rate of 

 conductivity is very low. Gotch and Burch photographed the 

 diphasic wave in frog's nerve, with reduced velocity of conduction, 

 on the capillary electrometer. 



The diphasic character of the electromotive effects of rhythmi- 

 cal tetanisation can easily be seen in Waller's galvanometer 

 photographs. The curves show that the negative phase is often 



FIG. 141. Diagram of diphasic variation of electrical potential at two points of a nerve after a 

 single excitation, measured by the rheotome. (Hermann.) The curves a b c d e f show 

 respectively the electrical variations from the points proximal and distal to the electrodes. 

 The diphasic curve traced by the coarser lines results from the algebraic sum of the preceding. 

 The spaces filled by cross lines, which represent the two phases of the wave, are approximately 

 equal according to Hermann. 



followed by a positive phase, directly the stimulation ceases. The 

 positive phase is seen particularly in cooled nerve, and in nerves 

 injured by preparation, or by long soaking in normal saline. The 

 negative phase is most evident after prolonged tetanisation and 

 the action of a small amount of C0 2 (Figs. 138 and 140). 



As for muscle, so for nerve, it is highly probable that the 

 negative phase of the current of action may be the expression of 

 a katabolic or disintegrative process, and the positive phase, of an 

 anabolic or reintegrative process. 



After all that has been said of the current of action it is 

 natural to regard it as the external sign, and to a certain extent 

 the measure, of the active state of a nerve, i.e. of its excitation. 

 But it must not be thought that the electrical phenomenon con- 

 stitutes the whole or the essential part of excitation. In the 

 present state of our knowledge we must, while holding the current 

 of action to be concomitant with the active state of the nerve, 

 keep the two phenomena distinct ; since, as we shall see, the 



