ADVANCED EXPERIMENTAL PHYSIOLOGY 



291 



exerted by the muscle. The length of wire which undergoes torsion 

 can be adjusted by altering the horizontal length of the brass arm 

 carrying the axis; the smaller the muscle the greater this length 

 must be. 



Arrange the apparatus for stimulating a muscle directly with a single 

 maximal induction-shock, using the drum as a key in the primary 

 circuit. Prepare a single or double gracilis-semimembranosus prepara- 



Fio. 173. Isotonic and isometric lever. 



tion (p. 281), fix the bone of one end in the muscle clamp, and the lower 

 end, by means of a bent pin or very short thread, to the lever one inch 

 in front of its axis. Release the screw fixing the axis and see that it 

 works smoothly. Attach a weight of 50 grms. to the lever near its axis 

 and adjust the muscle clamp vertically so that the lever is horizontal. 

 Record a single contraction on a rapidly revolving drum, mark a base 

 line and the point of stimulation. Swing the writing point off the drum, 

 but do not move the base of the stand carrying the myograph. Now 

 remove the weight and attach the muscle to the lever just in front of 

 its axis. The muscle-clamp will need horizontal adjustment, so that 

 the muscle again lies in a vertical straight line with its point of attach- 

 ment to the lever. Adjust the length of the wire to the size of the 

 muscle, and with the lever horizontal firmly clamp the axis. The 

 muscle-clamp will probably need vertical adjustment, so that the muscle 

 may be taut but under no initial tension. Swing the- writing point on 

 to the drum ; it should exactly coincide wiih the old abscissa line, and, 

 if the base of the stand has not been moved, the point of stimulation 



