88 GENERAL PROPERTIES OF LIVING TISSUES 



(Fig. 22) against the paper below the point of 

 the muscle lever, and stimulate the muscle to 

 contract. 



Observe that the tuning fork now gives the 

 time intervals on the abscissa of the muscle 

 curve, from which the duration of the periods 

 of shortening and relaxation may be known. 

 Note also the difference in appearance of curves 

 recorded on a slow and a rapidly moving 

 surface. 



Measure the interval between the beginning 

 of contraction and the point of maximum 

 shortening. 



In your laboratory note-book write a critical 

 account of the muscle lever. 



Compare this account with the remarks which 

 follow : 



The object of the muscle lever is to write a 

 magnified record of the change in form of the 

 muscle. Usually the muscle is suspended in a 

 muscle clamp and its lower end attached to 

 the lever, which then records the shortening of 

 the muscle. The same lever may be used to 

 record the thickening of the muscle; in this 

 case the muscle is of course horizontal and 

 the lever rests upon it. For either purpose 

 the weight of the lever is an objection, for 

 it tends to prevent the muscle from begin- 



