xxxvir.] 



PENDULUM-MYOGRAPH. 



209 



the same as for the pendulum-myograph, the trigger-key of the 

 myograph being placed in the primary circuit. 



(a.) Cover the glass with glazed paper, smoke it, and fix it in 

 the frame. Push the plate to 

 one side, and fix it with the 

 catch. Close the trigger key 



(b.) Make a nerve-muscle 

 preparation, and arrange it to 

 write on the glass plate. Open 

 the secondary circuit. 



(c.) Press on the thumb- 

 plate (a), thus liberating the 

 spring, when the glass plate 

 shoots to the other side, when 

 the tooth (d) on its under 

 surface breaks the primary 

 circuit, and the muscle-curve 

 is recorded. 



(d.) Short-circuit the second- 

 ary circuit, push back the 

 plate, and fix it with the 

 catch; close the trigger-key, 

 and shoot the plate again to 

 record the abscissa. 



(e.) Make a time-curve. Push the plate back again, and fix it ; 

 close the trigger-key in order that the conditions may be exactly 

 the same as before set a tuning-fork in vibration (120 double 

 vibrations per second), and adjust its writing-style under the 

 abscissa. Shoot the plate again, and record the time-curve. 



FIG. 128. Arrangement for Estimating the 

 Time-Relations of a Single Muscular Con- 

 traction. B. Battery ; K. Key in primary 

 circuit; I. Primary, //. Secondary coil, 

 without a short-circuiting key ; I. Muscle- 

 lever ; e. Electro-magnet in primary cir- 

 cuit ; t. Electric signal ; St. Support ; RC. 

 Revolving cylinder. Introduce a short- 

 circuiting key into the secondary circuit. 



ADDITIONAL EXERCISES. 



3. Study the improved form of this instrument recently introduced by Du 

 Bois-Reymond in which the glass plate is set free : and the tuning-fork vibra- 

 tions are recorded simultaneously when a handle is pressed. It has a simple 

 mechanism for adjusting the writing-styles for the muscle and abscissa. 



4. Analysis of Twitch on a Revolving Drum. 



(a.) Arrange the drum to move at a fast speed (50 cm. per sec.) 

 (b.) Arrange an induction coil for single B. shocks, the secondary circuit 

 short-circuited, and arranged to stimulate a nerve attached to a muscle placed 

 in a moist chamber, or on a crank-myograph, as directed for the foregoing 

 experiments. In the primary circuit introduce, besides the spring-key, an 

 electro magnet with a marking lever (figs. 116, 128, e), and cause its point to 



