AND ITS MODE OF ACTION. 427 



to another. A straight horizontal line (b , is also traced upon the card 

 by the extremity of a slender steel lever, the other end of which forms 

 a part of the galvanic circuit. The closure of the circuit is accom- 

 plished by a movement which pushes aside this lever, and thus causes a 



Fig. 146. 



DIAGRAM OF THE REGISTERING APPARATUS, according to the plan of Marey. 

 a. Undulating line traced by the diapason, which marks the time consumed by the card in 

 moving from one point to another, b. Line traced by the first lever, forming part of the 

 galvanic circuit, c Line traced by the second lever, which is moved by the contraction of 

 the muscle, d. Deviation of the line 6, indicating the closure of the galvanic circuit and the 

 stimulation of the nerve, e. Deviation of the line c, indicating the muscular contraction. 



deviation (d ) in the line traced by its extremity. This deviation registers 

 upon the card the instant of the closure of the circuit, and consequently 

 that of the stimulation of the nerve. The muscle used for experiment 

 is fixed in position, with its tendon attached to a second lever in such a 

 way that any muscular contraction will draw aside its free extremity. 

 This lever traces upon the card a second straight horizontal line (c) 

 parallel to the first ; and when the muscle contracts, the line is devi- 

 ated, as at (e), by the lateral movement of the lever. 



Thus when the experiment has been performed, there are left upon the 

 surface of the card two deviations d and e, one of which represents the 

 stimulation of the nerve, the other the muscular contraction; and between 

 the two is included a certain interval. The number of undulations in 

 the diapason-trace (a), corresponding to this interval, gives the time 

 which has elapsed between the stimulation of the nerve and the contrac- 

 tion of the muscle. In the example shown in Fig. 146, as the interval 

 between the deviations includes 13 simple variations, of which 500 

 would represent one second, the time occupied is 0.026 of a second. 

 By this means, intervals of time of very short duration may be registered 

 and compared with accuracy. 



Subsequently to the experiments upon separated nerves and muscles 

 in the lower animals, investigations of a similar kind were extended to 

 the human subject during life. In the experiments of Baxt, 1 this was 

 done by applying the electrodes to the surface of the skin immediately 

 over the situation of the median nerve, and at varying distances from 

 the muscles to which its fibres are distributed. The nerve was thus 



1 Monatsbericlit dor Eoniglichen Freussischen Akademie, April, 1867, and 

 March, 1870. 



