XXXIV.] THE GRAPHIC METHOD. 199 



circuit. There may be no contraction at either M. or B. Close 

 the secondary circuit key. 



(6.) Open the short-circuiting key, gradually push up the secondary 

 coil, and break the primary circuit by means of the key in it. 

 Observe when the first feeble single contraction or twitch is 

 obtained = minimal contraction. Make the primary circuit, there 

 is no contraction. The break shock is stronger than the make. 

 Record under each contraction whether it is a make (M.) or break 

 (B.) shock, and the distance in centimetres of the secondary from 

 the primary coil. The minimal contraction may first be obtained 

 when the secondary coil is 35-40 cm. from the primary. Move 

 the drum a short distance with the hand ; the lever inscribes a base 

 line or abscissa. 



(c.) Push up the secondary coil .5 cm. at a time. Test the effect 

 of the make and break shocks, after each test moving the cylinder 

 with the hand, and recording the result as to M. or B., and the 

 distance in centimetres of the secondary from the primary coil. 

 After a time a M. contraction appears, and on pushing up the 

 secondary coil the M. contraction becomes as high as the B. 

 (fig. 117). 



FIG. 117. Contractions obtained with make (M.) and break (B.) induction shocks. The 

 numbers indicate the distance of the secondary from the primary coil. The cylinder 

 is stationary during each contraction and is then moved a little distance by hand. 



(rf.) Increase the stimulus by bringing the secondary nearer 

 the primary coil, and notice that the contractions do not become 

 higher = maximal contraction. In each case keep the M. and 

 B. contractions obtained with each strength of current close 

 together. Their relative heights can then be readily compared 

 (fig. 117). 



B. Twitch with Cylinder revolving (fast speed). Arrange 

 the experiment as in A, but allow the cylinder to revolve about 

 50 centimetres per second. 



(a. ) Select a strength of stimulus (break shock only) which is 

 known to cause a contraction, and while the cylinder is revolving, 

 cause the muscle to contract. 



