THE CRANK MYOGRAPH. 



167 



9. The work done. After the tracing of B is dry, from the 

 abscissa draw vertical lines, or ordinates, and measure their height 

 in millimetres. Measure the length of the lever, and from this 

 calculate the actual amount of shortening of the muscle itself 

 Multiply this by the weight lifted, and the product is the work 

 done expressed in gram-millimetres. 



10. The Crank Myograph (Fig. 62) is fixed on a suitable sup- 

 port, so that it can be adjusted to any height desired. The 

 experiment is arranged in exactly the same way as for 7. 



(a.) Use one hind-limb of a pithed frog; pin the femur 

 firmly to the cork plate of the myograph covered with 

 blotting-paper moistened by normal saline, the tibia being 

 in line with the writing-lever. Or take the pithed frog, lay 

 it on the frog-plate of the myograph, expose the gastro- 

 cnemius, and proceed as above. Detach the tendo Achillis, 

 tie a stout ligature to its sesamoid bone, and fix the liga- 



1 



Fig. 62. Crank Myograph. W,W, Block of wood; M, muscle; F, femur; 

 P, pin to fix F ; L, lever ; WT, weight ; a, screw for after-load ; 

 C, cork ; B,B, brass box. (In this figure the fulcrum should be at the 

 angle of the crank.) 



ture to the short arm of the lever, add a weight of 20 

 grammes to the lever, and see that the lever itself is hori- 

 zontal. Thrust two fine wires the electrodes from the 

 du Bois key in the secondary coil, through the upper and 

 lower end of the gastrocnemius muscle; 



(6.) Arrange the style of the lever so that it writes on the 

 cylinder, and repeat the experiments of either A or B, or 

 both. 



