254 Mr. Graham Brown and Prof. C. S. Sherrington. [Mar.-16, 



sometimes changes its response so as to yield primary extension even after 

 a comparatively small number of repetitions. 



Reversals of this kind tend in our experience to occur more frequently 

 with E points than with F points. The reversal may evidence itself as 

 relaxation of one muscle along with contraction of the other, or it may be 



Experiment 13, Callothrix, 19.2.12. — Eecord of a series of four successive stimulations 

 of an extensor (" E ") point, each stimulation being of a duration of about 2 sees., with 

 intervals of 2 sees, between successive stimuli. In this record the movements of the 

 flexor muscle alone are reproduced. At the first application of the stimulus the flexor 

 relaxes. In the succeeding interval there is a partial recovery of the flexor tonus. The 

 second stimulus evokes relaxation, followed by contraction, through the period of stimula- 

 tion. The third gives a shorter phase of relaxation and a greater contraction. At the 

 fourth application of the stimulus there is a response of almost pure contraction. 



In this and in all succeeding records the rise of the curve denotes contraction of the 

 recorded muscle, and the fall relaxation. Below the muscle tracings are two signal lines. 

 In these the fall of the signal denotes the beginning of stimulation and the rise the end of 

 stimulation. These points are marked by capital letters (C, D, E, F, A, B, X, Y), and on 

 the muscle tracings ordinates which correspond in time to the signal marks have been 

 drawn. The ordinates bear the corresponding small letters. In the signal lines the 

 numerals give the relative strengths of stimulus as measured by the distance in centi- 

 metres between the primary and secondary coils. The lowest line marks time in seconds. 



In all succeeding figures the movements of both of the antagonistic muscles are repro- 

 duced. The upper tracing is that obtained from the flexor — supinator longus ; and the 

 lower tracing is that obtained from the extensor — the humeral head of the triceps. A 

 millimetre scale has been drawn upon the tracing before it was varnished, and is 

 therefore reduced in the same ratio as the remainder of the record. In many other 

 records there are additional ordinates drawn upon the two muscle tracings, to demon- 

 strate the correspondence in time of different parts. These are numbered in Arabic 

 numerals. The letters " CP," sometimes present in the signal lines, mean that in these 

 records the primary current was broken immediately after the cutting of the secondary 

 circuits. 



