SAPIDITY OF NERVOUS CONDUCTION. 101 



interval of pose, or the length of time between the excitation 

 of a muscle and the commencement of its contraction, 1 he esti- 

 mated the rapidity of conduction in the motor nerves of the 

 frog at about eighty-five feet per second. 9 The results ob- 

 tained by Marey upon frogs give a much slower rate of 

 nervous conduction. These were followed, however, by the 

 observations of Helmholtz and Baxt on the human subject, 

 which are, of course, the most interesting of all. 



The process devised by Marey is beautifully simple. He 

 employed, to estimate small fractions of a second, a cylinder 

 graduated in the following manner: An ordinary tuning- 

 fork, vibrating, say, five hundred times per second, is so 

 arranged that a point connected with one of its arms is made 

 to play against a strip of blackened paper. As the paper 

 remains stationary, the point makes but a single mark ; but 

 when the paper moves, as the point vibrates, a line is pro- 

 duced with regular curves, every curve representing T J 7 

 of a second. Now, if a lever be attached to a muscle, and 

 be so arranged as to mark upon the paper, moving at the 

 same rate, the instant when contraction takes place, it is evi- 

 dent that the interval between two contractions produced 

 by stimulating the nerve at different points of its course will 

 be most accurately indicated ; and if the length of the nerve 

 between the two points of stimulation be known, the differ- 

 ence in time will represent the rate of nervous conduction. 3 



In experiments upon frogs, the leg is prepared by cutting 

 away the muscles and bone of the thigh, leaving the nerve 

 attached. The lever is then applied to the muscles of the 

 leg and the stimulation is applied successively at two points 

 in the nerve, the distance between them being carefully 

 measured. The results obtained in this way showed a rate 



1 See vol. iii., Movements, p. 472. 



8 Comptes rendus, Paris, 1851, tome xxxiii., p. 262. 



3 MAREY, Du mouvement dans les fonctions de la vie. Revue des cours scien- 

 tijiques, Paris, 1865-'66, tome iii., p. 346, et seq.; and, Du mouvemenf, etc., Paris, 

 1868, p. 410, et seq. 



