XO Buchanan 



particular arrangement adopted of connecting the muscle with the electro- 

 meter, always denotes that the contact between the proximal electrode and 

 the muscle was during that time (galvanometrically) negative to the other 

 contact. When the mercury is moving most quickly, when the rise in the 

 record is steepest, this negativity is greatest. When the mercury is moving 

 most slowly (as indicated, for instance, by a summit on the curve), this nega- 

 tivity is least, and the difference of potential is either just about to cease, or 

 is being reversed. A descending curve, according to its steepness, i.e. an 

 abostial movement of the mercury, according to its quickness, denotes 

 either that the distal contact is now negative to the proximal, or that there 

 is still no difference of potential between them and that the meniscus is 

 returning in its own time to its original position. It means the former before 

 it means the latter when the contacts are made with two parts of the muscle, 

 each of which in turn becomes electrically, then mechanically, active. 



If the electrical disturbance produced by the excitation of the motor part of 

 the nerve is over, under both electrodes as it usually is, before that produced 

 by the excitation of the sensory part has begun to manifest itself under 

 the proximal electrode, the beginning of this second electrical event is 

 luarked on the curve either by a fresh rise (as in figs. 1, B. and 2, A) or by 

 a checking of the course of the descending curve. 



Having learned to identify the reflex effect in the records, there is no 

 difficulty in ascertaining the time which elapsed between the moment at 

 which the primary direct response reached the first recording spot on the 

 muscle, and that at which the reflex effect reached the same spot ; i. e. the 

 time taken for the impulse to travel a known length of nerve to the cord, and, 

 after passing through the cord, to travel the same length of nerve back again. 



The shortest time interval between the arrivals of the two effects at 

 the proximal electrode in those preparations which were not under the 

 influence of any drug was 14o- ; but it was only in one response (the first) 

 in one preparation [Exp. 15] that I obtained a value so low,^ it being about 

 1<T longer in the three other responses recorded with the same preparation. 

 In a record obtained in one other experiment [Exp. 31], the interval 

 appeared to be equally short, but this was an experiment in which the 

 comparison of the records taken with the exciting current in opposite 

 directions showed that there was a block at the kathode which it took the 

 impulse Icr to overcome in going straight to the muscle, so that probably 



1 The measurements on which the time vahies in all my experiments depend were 

 made for each record not only by myseh' but independently by another person who knew 

 nothing about their !-ignificance or the conditions under which the experiments were made. 

 (I have been enabled to obtain this, and other, valuable assistance in the measurement of 

 records, by the kindness of Dr Osier.) On each occasion in which our final results 

 differed by more than 0"5o-, and especially if there were any relative difference in the 

 values we each obtained in any one experiment, the whole process was gone over again by the 

 one or the other of us. The number of thousandths of a second in the time values given 

 in the text or in the tables may therefore be relied upon, but the fractions of a thousandth, 

 when given, make no profession of being absolutely accurate. 



