ix ELECTRICAL EXCITATION OF NERVE 133 



use of. Since, however, these do produce vigorous twitches, the 

 conclusion for transverse inexcitability of nerve, based upon 

 observations with weaker currents, seems to be insufficiently 

 established. Hitzig (16) ancI_.Filehne (16) employed two strips 

 of clay, mixed with 1 ' ^ salt solution, for leading in the current. 

 The broad thin edges of the clay strips were applied on both 

 sides to the nerve, and the strength of current appropriately 

 graduated. Here again there was inexcitability to transverse 

 passage. 



As in muscle, the best method is to lay the nerve in an 

 " exciting chamber " filled with indifferent conducting fluid 

 (physiological saline), through which the current is sent from two 

 opposite points or surfaces (Fig. 184). The results and con- 

 clusions of the several experimenters are, notwithstanding simi- 

 larity of method, very divergent. A. Fick, jun., (16) affirms the 

 complete inexcitability of nerve to pure transverse passage of 

 current, confirming du Bois-Beymoud's conjecture (16), that with 

 approximately equal conditions the influence of the angle at 

 which the current passes must be about equal to its cosinus. 

 Tschirjew (16), on the contrary, denies the influence of the 

 current angle, and regards the excitability of the nerve to trans- 

 verse and longitudinal passage of current as equal. It is 

 important to remember that (as was first pointed out by 

 Hermann, 17) the resistance of nerve is very different in the 

 longitudinal and transverse directions, being much higher in the 

 latter than in the former. If a layer of parallel frogs' nerves 

 between two square glass plates is traversed by current, first 

 lengthways and then across, the transverse resistance, as measured 

 by Wheatstone's method, is found to be about five times as great 

 as the longitudinal resistance (according to Hermann, the first 

 exceeds the resistance of the mercury by 12^- million times, the 

 second by only 2^- million). Similar differences exist in striated 

 muscle, and appear in both cases to be bound up with the normal 

 vital properties of the tissue, since they diminish considerably 

 after mortification has set in. (According to Hermann, the ratio 

 in nerve sinks, even with heating to 50 C., from 1:5 to 1 : 2 - 4.) 



With regard to these facts, it is clear that when the nerve 

 enclosed in the exciting chamber is longitudinally traversed, a 

 greater fraction of the current must pass through it than when 

 the lines of current are in the transverse direction, and it only 



