252 PRACTICAL PHYSIOLOGY. [L. 



through the electrodes away from the muscle (b). Unshort-circuit 

 the secondary circuit, and shoot the glass plate, when another 

 curve will he inscribed, this time a little later than the first one. 



(e.) Replace the glass plate, close the trigger-key, short-circuit 

 the secondary circuit, and shoot the plate. This makes the abscissa. 



(/.) Replace the glass plate, close the trigger-key, and bring the 

 tooth of the glass plate (3) just to touch the trigger-key ; raise the 

 writing-lever to make a vertical mark. This indicates the moment 

 when the stimulus was thrown into both points of the nerve. 



(#.) Remove the moist chamber, push up the glass plate, close 

 the trigger-key, and arrange a tuning-fork vibrating 250 D.V. per 

 second to write under the abscissa. Shoot the plate again and the 

 time-curve will be obtained. Fix the tracing, draw ordinates from 

 the beginning of the curves obtained by the stimulation of a and b 

 respectively, measure the time between them from the time-curve 

 (this gives the time the impulse took to travel from b to a), and 

 calculate the velocity from the data obtained. 



Example. Suppose the length of nerve to be 4 cm., and the time 

 required for the impulse to travel from b to a to be yi^ sec. Then 

 we have 4 : 100 : T ^" : ^V'> or 3 metres (about 98 feet) per 

 second, as the velocity of nerve-energy along a nerve. 



2. Repeat the observation with the pendulum-myograph. 

 Practically the same arrangements are necessary. 



If it be desired to test the effect of heat or cold on the rapidity 

 of propagation, the nerve must be laid on ebonite electrodes, made 

 in the form of a chamber, and covered with a lacquered copper 

 plate on which the nerve rests. Through the chamber water at 

 different temperatures can be passed, and the effect on the rate of 

 propagation observed. 



3. Velocity of Motor Nerve-Impulse in Man. 



(a.) Use a pendulum-myograph. Connect two Darnell's cells 

 with the primary circuit of an induction coil and interpose in the 

 circuit the trigger-key of the myograph, which the pendulum opens 

 in swinging past. Place a short-circuiting key in the secondary 

 circuit, and to the short-circuiting key attach a pair of rheophores 

 moistened with strung solution of salt. 



(b.) Arrange Marey's "pince myoyrapliique " (fig. 1 5 1) to compress 

 the adductor muscles of the thumb when the latter is in the 

 abducted position. Connect the " pince " by means of an india- 

 rubber tube with a Marey's tambour (fig. 150) arranged to record 

 its movements on glazed paper fixed to the plate of the pendulum- 

 myograph. 



(c.) The nerve supplying the adductor muscles of the thumb 



