116 EXERCISE XVIII 



the break-shock kathode this time distal to, i.e. nearer to the muscle than, the 

 anode.] Leave the electrodes and nerve so arranged, taking care that they are 

 well isolated from the edges of the wound. Push the secondary coil away 

 from the primary as far as the 35 cm. mark on the inductorium scale. 

 Repeat the manoeuvre for finding the break-shock threshold stimulus as before, 

 and note the value obtained. Then push the secondary coil nearer to the 

 primary by some 8-10 cm., and obtain a record of the contraction to the break- 

 shock given by the automatic striker, using the same manoeuvre as before. 

 Swing oif the myograph from the drum-surface. Then stop the driving-gear 

 for the drum. 



Obs. 86. IX. To measure the latent period between stimulus delivery and 



Measurement beginning of the contraction. Close the bridge-key. Close the primary key. 



reflex and lurn the drum by the hand slowly and bring the striker on the drum- spindle 



twitch. close to the primary key lever. Rotate writing-lever standard so that the 



writing-point again touches drum. Push the secondary coil 5 cm. or so 



closer to the primary. Open the bridge-key. Then very slowly rotate the 



drum slightly so that drum-spindle striker just opens the primary key. The 



contraction which occms marks on the drum the ordinate corresponding to 



the moment when the stimulus is delivered by the drum-striker's opening of 



the primary key. 



Compare the two contraction curves, reflex and peripheral, obtained and 

 note the difference of the latencies. 



Bring near to the drum-surface a 100 sec. tuning-fork clamped firmly to 

 a vertical rotating standard, the rotation carrying as far as a check. Adjust 

 to drum-surface when the fork standard is up to the check. Set the drum 

 going, and, when it is in full course, set fork vibrating and swing the recording 

 style of the fork to the drum-surface, i. e. up to the check. This measures 

 speed of drum-surface and therefore of the time-relations of the myograms and 

 their latencies ; after one revolution of drum, swing fork off it. 



X. Repeat § VI ; note that the contraction resulting from fall of lever is 

 now absent, i.e. the contraction was reflex. 



ANNOTATION 



Ohs. 83. For observations on the pro- reflex contraction than that of the peripheral 



prioceptive reflex of tibialis anticus see paper contraction cannot be accounted for wholly 



by Chuai Asayama, 1916, Quart Jnl. of by the greater length of nerve- trunk which 



Experim. Physiology, vol. ix, p. 265. the impulse has to travel in the former 



Ohs. 84-6. The longer latency of the case ; the difference is too great, and indicates 



