Q Buchanan 



the slit, a wheel-like cardboard disc (called by Dr Garten of Leipzig, who 

 first introduced it for this particular purpose, an " episkotister ") was 

 rotating in front of it at such a speed that the light was obscured by a 

 spoke between 700 and 850 times a second. The exact rate at which the 

 spokes were passing the slit at the time it was taken could always be 

 determined with accuracy on the developed photograph, either by means 

 of the record on the plate of an electromagnetic signal set into vibration 

 by a 100 fork, or by the vibrations of a rod in connection with the break- 

 key inside the dark-box, the primary function of which was to mark on 

 the plate the moment at which the nerve was excited. The value of 

 O'l second was determined (with the aid of the 100 fork record) in terms 

 of the vibrations of this rod as they appear on the photographs on several 

 occasions, and was found to be quite constant (so long, of course, as no 

 alteration was made in the length of the vibrating rod). Whenever the 

 key for any reason had to be interfered with, a fresh estimation of this 

 value was again made. The number of spokes obscuring the light in 

 0"1 second, as determined by the lines on the plate, was counted, and the 

 value of the interval between two such lines, in time, was calculated for 

 every photograph. 



Two methods of distinguishing a reflex response in a record suggested 

 themselves, and, accordingly, when the preparation was ready, the experi- 

 ment was continued in one of two ways. In the one case, the strength 

 of induction shock to the nerve required for a " maximal " contraction 

 of the muscle was first determined. Then, the preliminary experiments 

 having shown that the maximal electrical effect is produced by the same 

 strength of stimulus as the maximal mechanical efl'ect, the electrical re- 

 sponse to a stimulus of this strength, or to one but little stronger than 

 it, was recorded. By means of the graduated scale with which the induc- 

 torium was provided, the secondary coil was next so far pushed up that 

 the induction current might be three or four times as strong, and another 

 record was taken. Responses to just maximal and to supra-maximal 

 stimuli were then recorded alternately three or four times, sometimes also 

 those to still stronger stimuli, in which case one record at least was taken 

 with the direction of the current reversed. 



Two consecutive records obtained in one experiment of this kind are 

 reproduced in fig. 1. (A) represents the response to a stimulus just 

 over the "maximal," (B) that to one three times as strong. The direct 

 response of the muscle to stimulation of the efterent part of the nerve 

 began under the proximal electrode, in each case four-thousandths of a 

 second (4(t) after the excitation of the nerve. In the second record there 

 is seen in addition a much smaller effect, the position of which shows that 

 the muscle was again electrically active under the proximal electrode 2S<t 

 later than when it became so the first time, 27cr therefore after the 

 excitation. In the particular experiment to which these records refer it 

 was only in the two first responses to the supra-maximal stimulus that this 



