102 NEKVOUS SYSTEM. 



of conduction of from thirty-six to forty-six feet per second ; 

 but these are not regarded by Marey as invalidating the 

 estimates by Helmholtz, in view of the various conditions by 

 which the rapidity of conduction is modified. 1 



Employing the myograph of Marey, Baxt, in the labora- 

 tory of Helmholtz, has succeeded in measuring the rate of 

 nervous conduction in the human subject. In these experi- 

 ments, the swelling of the muscle during contraction was 

 limited by enclosing the arm in a plaster-mould, and noting 

 the contraction through a small opening. By then exciting 

 the contraction by stimulating the radial nerve successively 

 at different distances from the muscle, the estimate was 

 made. The rate in the human subject was thus estimated at 

 one hundred and eleven feet per second. 2 The latest experi- 

 ments on this subject by Helmholtz and Baxt, in which great 

 care was taken in the adjustment of the apparatus, showed a 

 mean of rapidity for the motor nerves, in man, of about two 

 hundred and fifty-four feet per second. These observations 

 were made in the summer of 1869 ; and the difference in the 

 results is in part explained by the fact, which was ascertained 

 experimentally at that time, that a high temperature in- 

 creases, and a diminished temperature retards the velocity 

 of nervous conduction. 3 It has been further shown by Munk, 

 that the rate of conduction is different in .different portions 

 of the nervous trunk ; the rapidity progressively increasing 

 as the nerve approaches its termination. 4 



Helmholtz, Du Bois-Reymond, B Marey, and others, have 



1 MAREY, Du mouvement, etc., Paris, 1868, p. 433. 



2 BAXT, Versuche uber die Fortpflanzungsgeschwindigkeit der Reizung in den 

 motorischen Nerven des Menschen. Monatsbericlde der kdniglich Preussischen 

 Akademie der Wissenschaften zu Berlin, aus dem Jahre, 1867, Berlin, 1868, S. 233. 



3 HELMHOLTZ UND BAXT, Fortpjlanzungsgeschwindigkeit der Erregung in 

 Bewegungsnerven. Der Naturforscher, Berlin, 1870, Bd. Hi., S. 230. 



4 MUNK, Untersuchunaen uber die Zeitung der Erregung in Nerven. A rchiv 

 fur Anatomie, Physiologic, und wissenschaftliche Medecin, Lsipzig, 1864, S. 798, 

 et seq. 



6 Du BOIS-REYMOND, Vitesse de la transmission de la volonte et de la sensation d 

 iravers les nerfs. Revue des cours scientifiques, Paris, 1866-'67, tome iv., D. 37 



