. Kirkes' handbook of physiology . Fig. 352.—Simple Form of Pendulum Myograph and Accessory Parts. A, Pivot upon whichpendulum swings; B, catch on lower end of myograph opening the key, C, in its swing; D, a spring-catch which retains myograph, as indicated by dotted lines, and on pressing down the handle ofwhich the pendulum swings along the arc to D on the left of figure, and is caught by its spring. paratus adjusted as in figure 351. Prepare a recording cylinder for makingvertical records of the contractions. Adjust the writing point of the musclelever to the drum and move the drum by hand
. Kirkes' handbook of physiology . Fig. 352.—Simple Form of Pendulum Myograph and Accessory Parts. A, Pivot upon whichpendulum swings; B, catch on lower end of myograph opening the key, C, in its swing; D, a spring-catch which retains myograph, as indicated by dotted lines, and on pressing down the handle ofwhich the pendulum swings along the arc to D on the left of figure, and is caught by its spring. paratus adjusted as in figure 351. Prepare a recording cylinder for makingvertical records of the contractions. Adjust the writing point of the musclelever to the drum and move the drum by hand 1 cm. after each succeedingcontraction. Set the secondary coil of the induction apparatus so that it willbe too weak to produce a stimulus. Now attempt to stimulate the muscle, THE EFFECT OF FATIGUE 497 then move the induction coil toward the primary i cm. at a time and repeatuntil the first slight contraction appears. Continue to slide the secondary coiltoward the primary, stimulate at each new position, moving the drum forward. FlO. 353-—Record of a Simple Contraction of the Gastrocnemius of the Frog. Time in .01of a second. St, Moment of stimulation. Record taken on a rapid drum that was provided withan automatic key. for each stimulus as directed, until a series of contractions is obtainedthrough the range of variation of induction of which the apparatus is capa-ble, usually twenty to thirty contractions. A typical tracing, figure 326, shows that as the strength of the stimulus isincreased the amplitude of the contractions quickly mounts from the minimalto a maximal, after which all further increase in the strength of the stimulusproduces contractions of practically the same height. The first perceptiblecontraction is called the minimal contraction, the strength of the current whichproduced it a minimal stimulus for that preparation. The contractions ofthe greatest amount are called maximal contractions. The weakest stimuluswhich produces a maximal contraction is called
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