APPENDIX I. 109 



in the diagram, and through the part B farther from 

 the muscle, by means of the wires 5 and 6, two sets 

 of observations are obtained, the corresponding 

 figures of which differ from each other by a small 

 but constant quantity, independent, moreover, of the 

 additional charge placed upon the scale-pan. This 

 difference obviously indicates the time required by 

 the nervous agent for travelling from B to A, and 

 the distance between A and B being known, the rate 

 of propagation of the stimulation or the velocity of 

 the nervous agent can easily be calculated. 



This velocity, in Professor Helmholtz's experi- 

 ments, has been found to be 26*4 metres (86'6 feet) 

 in one second.* The reason why on stimulating 

 the nerve the time of latent stimulation appears a 

 little longer than on stimulating the muscle itself, 

 is now also evident. It is owing to the time which 

 elapses during the passage of the nervous agent from 

 the stimulated part of the nerve-tubes to their ter- 

 mination in the muscle. 



Professor Helmholtz's Experiments with the Myo- 

 graphion. Soon after Professor Helmholtz had thus, 

 for the first time, succeeded in determining the 

 velocity of the nervous agent, he devised another 

 method for obtaining the same result in a manner 

 more simple and more adapted to a variety of pur- 

 poses. 



As before, the gastrocnemius muscle is caused to 

 lift a lever by its contraction, but this time with 

 the view of making the muscle itself register the 



* Job. Mailer's Archiv filr Anatomie, Physiologie und wis- 

 senschaftliche Medicin. Berlin, 1850. S. 276. 



