MINIMAL AND MAXIMAL STIMULI 



5 2 7 



directly by means of the secondary current of the induction coil, with the ap- 

 paratus adjusted as in figure 351. Prepare a recording cylinder for making 

 vertical records of the contractions. Adjust the writing point of the muscle 

 lever to the drum and move the drum by hand i cm. after each succeeding 

 contraction. Set the secondary coil of the induction apparatus so that it will 

 be too weak to produce a stimulus. Now attempt to stimulate the muscle, 

 then move the induction coil toward the primary i cm. at a time and repeat 

 until the first slight contraction appears. Continue to slide the secondary coil 

 toward the primary, stimulate at each new position, moving the drum for- 



FIG. 352. Simple Form of Pendulum Myograph and Accessory Parts. A, Pivot upon 

 which pendulum 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 of \vhich the pendulum swings along the arc to D on the left of 

 figure, and is caujjht by its spring. 



ward for each stimulus as directed, until a series of contractions is obtained 

 through 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 is 

 increased the amplitude of the contractions quickly mounts from the minimal 

 to a maximal, after which all further increase in the strength of the stimulus 

 produces contractions of practically the same height. The first perceptible 

 contraction is called the minimal contraction, the strength of the current 

 which produced it a minimal stimulus for that preparation. The contractions 

 of the greatest amount are called maximal contractions. The weakest 



