99 



the length of the lever in millimeters ; then measure from the 

 point of attachment of the muscle to the fulcrum and divide 

 the total length by this and the result will give the degree of 

 magnification of the shortening of the muscle. 



342. Work Done During a Single Contraction. 

 Arrange a gastrocnemius to record on a cylinder, but record 

 only the "lift," the cylinder being stationary, move the 

 cylinder by the hand as required. On the lever under the 

 muscle attachment place weights of known value. With each 

 twitch the muscle lifts the weight, and thus does a certain 

 amount of work which is easily calculated. 



(a). Measure the height of the tracing from the base line 

 or abscissa. This is conveniently done by a millimeter scale. 

 The work which is done (w) is equal to the load (1) multi- 

 plied by the height (h) to which it is lifted ; w=lh. But, of 

 course, a long lever being used the tracing is much higher 

 than the actual shortening of the muscle. 



(b). To determine the exact amount of the lift, one must 

 know the length of the lever and the ratio between its arms. 

 Suppose the one to be ten times as much as the other, then 

 the total work in gram-millimeters must be divided by ten. 



Try different weights always using the same stimulus. 

 It will be found that at a certain point there will be a maxi- 

 mum contraction after which the contractions will become 

 weaker, because of the greater load and fatigue. Calculate 

 the amount of work done at the maximum contraction. 



343. Record of the Thickening of a Muscle. Pre- 

 pare a nerve-muscle preparation and lay it on a glass plate, 

 keeping it well moistened with the saline solution. Arrange 

 the battery and induction coil as before. Adjust the heart 

 lever (such as used in recording the beat of the frog's heart) 

 so that the vertical portion of the lever rests upon the belly of 

 the muscle- Use the break and then the make shocks as be- 

 fore. Compare these curves with the others. The drum 

 should revolve at its fastest rate. 



'^ ^ CL^ 



