CONDUCTIVITY 129 



and the motor nerves of man 34 meters. Other investigators 

 have obtained quite different results; Hirsch, for the sensory 

 nerves of man, 34 meters ; Schelske, for the same, 25-33 meters ; 

 De Jaager, 26 meters ; v. Wittich, 34-44 meters, and Kohlrausch, 

 56-225 meters ; v. Wittich for the motor nerves of man, 30 meters ; 

 Piper^ finally in the most recent investigations about 120 meters 

 in the second. 



These differences may be explained in a large measure by the 

 variety of the methods used, in part also by the difference in the 

 structures. The methods employed for the study of the velocity 

 have also been used to solve the question, whether the velocity of 

 the excitation wave in its course over the nerve meets with a 

 decrement as it moves further and further away from the point 

 of stimulation. Here the endeavor was made to study the differ- 

 ence in time of the latent period, which is observed by the indi- 

 cator, when the nerve is stimulated at two points at different dis- 

 tances from the muscle, used as an indicator, or from the wires 

 leading the current to the indicator. The more recent investiga- 

 tors, as Rene Du Bois-Reymond,- Engelmann,^ G. Weiss,* have 

 arrived at the same conclusion, that the rate of conductivity in 

 the medullated nerve under normal conditions is the same at all 

 distances from the point of stimulation. (Figure 20.) 



The medullated nerve shows, therefore, under normal condi- 

 tions neither a decrement of its conductivity, nor of its irritability, 

 as the distance of the wave of excitation increases from that of 

 the position of stimulation ; this means, in other words, that excita- 

 tion is conducted with the same intensity with which it is started, 

 and with a constant rate throughout the entire course of the 

 nerve. 



There is, nevertheless, a third point of considerable difference 



1 Piper: "Ueber die Leitungsgeschwindigkeit in dem markhaltigen menschlichen 

 Nerven." 



The same: "Weitere Mitteilungen fiber die Geschwindigkeit der Erregungsleitung im 

 markhaltigen menschlichen Nerven." Pfliigers Arch. Bd. 127, 1909. 



2 R. Du Bois-Reymond : "Ueber die Geschwindigkeit des Nervenprincips." Arch, 

 f. Anat. u. Physiol, physiol. Abt. Suppl. 1900. 



ZEngelmann: "Graphische Untersuchungen uber die Fortpflanzungsgeschwindig- 

 keit der Nervenerregung." Arch. f. Anat. u. Physiol, physiol. Abt. 1901. 



4 G. Weiss: "La conductibilite et I'excitabilite des nerfs." In Journ. de Physiol, 

 et de Pathol, generale 1903. 



