FLEXOR REFLEXES 



115 



shifting the position of the secondary coil on the inductorium scale to 

 ascertain the weakest break-shock which excite?, and taking care to strike 

 open the short-circuit key with approximately the same speed each time. Note 

 the threshold stimulus thus determined. 



VII. B. Shift the secondary coil towards the primary to a point where 

 the break-shock, on striking open the bridge-key with the finger as before, 

 evokes a reflex contraction which raises the writing-point of the lever 3-4 cm., 

 as written with the stationary drum. Withdraw the lever-point slightly 

 from the drum-surface by rotating the lever-standard. Raise the primary 

 circuit key out of the course of the revolving striker of the drum-spindle. 

 Set the drum running. Bring the writing-point into contact with the drum- 

 surface again by rotating the lever-standard up to its check-stop. When the 

 drum has given several revolutions choose a moment when the striker has 



Text-fig. 40. Comparison of maximal twitch with reflex contraction in response to 

 a single break -shock applied to afferent nerve ; tibialis anticus muscle, decapitate 

 preparation (E. Barnard and C. H. Terry), m, contraction in response to break-shock 

 applied to motor nerve ; r, reflex response to break-shock applied to afferent nerve, 

 ipsilateral popliteal ; the short vertical arc marks moment of application of stimulus in 

 each case ; vibrations of tuning-fork 100 p. sec. above. 



just passed the place where it would meet the primary circuit key were it 

 lowered, and lower 'that key quickly and quietly as far as the stop on it allows, 

 the short-circuit key of the secondary circuit still remaining closed. Then at 

 once open the short-circuit key. The reflex contraction is recorded on the 

 drum. Then rotate the lever-standard slightly back again to withdraw the 

 lever-point from the drum-surface, and finally reclose the short-circuit key. 

 Do not stop the drum. 



VIII. Remove the electrodes from the tibial nerve. Ligate the peroneal Obs. 85. 

 nerve as high up the thigh as the wound allows and cut the nerve central to Twitchjcontrac- 

 the ligature. Apply the electrodes to the nerve distal to the ligature. 



Q 2 



pp, tion compared 



Lrlace ^jth reflex. 



