THE MYOGRAPH. I2/ 



2. The Curve of a Single Contraction, or Twitch. Pith a 



frog and place it on its belly on the myograph plate. After preparing and 

 attaching the muscle as above directed, expose the sciatic nerve, and place the 

 electrodes under it. Adjust the style of the lever so as to touch the smoked 

 surface. Open the key of the primary circuit and set the clock in motion. 

 A line is drawn by the style the abscissa of the future curve. As soon as 

 the fly has attained its maximum expansion, close both keys of the primary 

 circuit. At the moment the cylinder comes into contact with its key and 

 opens it, a curve is inscribed. Stop the clock and prepare for a second obser- 

 vation by giving a single or half turn to the pinion, and draw a second curve 

 similar to the first, and so on, until a series of parallel and similar curves has been 

 drawn. To observe the effect of exhaustion arrange the apparatus so that, while 

 the muscle is excited at each revolution, every tenth curve only is recorded. 



3- Influence Of Veratrin. Inject a drop of o-i per cent, solution 

 of Veratrin into the lymph sac of a brainless frog. After twenty minutes, 

 destroy the spinal cord and inscribe one or more muscle curves, and compare 



hem with those previously obtained. 



If in this, and in the preceding experiment, it be desired to employ the "nerve- 

 muscle preparation " rather than the entire pithed frog, the apparatus described 

 below may be substituted ; it can be made with simple materials, such as can 

 be procured anywhere. A thick brass wire is bent twice at right angles, in 

 the same plane. The middle part measures four inches, and each of the ends 

 two inches. On the middle part slides a cork bearing two centres, in which 

 an axis works. This axis bears a light lever about five inches long, which 

 moves in the plane of the two ends. The femur of the muscle-nerve prepara- 

 tion is attached by a wire to the upper end of the brass wire (called the 

 stretcher), and the tendon to the lever. A spiral spring, connecting the lower 

 end of the stretcher with the lever, serves to extend the muscle and opposes 

 its contraction. The nerve is enclosed in a tube provided with platinum elec- 

 trodes, which serves to protect it from evaporation. The whole apparatus is 

 supported as before (II, i), on an adjustable pillar, which is fixed to the 

 recording apparatus. 



4- Influence Of Temperature on the Form of the Curve of Single 

 Contraction. For studying this subject, the simple myograph just described 

 may be used. A spiral tube of metal of suitable form, must be prepared 

 and fixed to the stretcher so as to surround the muscle during the observation. 

 One end of the coil is connected by a flexible tube with a small reservoir of 

 water at a higher level, the other with a waste pipe. Make a muscle-nerve 

 preparation, pierce the femur with a fine awl, and pass a fine wire through 

 the hole and attach it to the upper arm of the stretcher. Secure the tendon 

 by a ligature to the lever and adjust the spiral spring, so that the lever is 

 parallel to the arms of the stretcher. With the aid of a fine silk thread 

 tied to its end, introduce the nerve with great care into the electrode tube and 

 close the latter with its cork. Adjust the writing lever. 



Having made the same arrangement as in the last exercise, pass a stream of 

 water through the coil at the ordinary temperature and inscribe a succession of 

 curves. Then repeat the observation, passing water through at various tem- 

 peratures from 5 C. to 30 C., observing the successive alterations in the form 

 of the contraction curve. 



