54 ELEMENTARY PHYSIOLOGY. IX. 



a time until the load is 200 to 300 grams, or until the 

 muscle fails to raise the weight. Mark opposite each 

 contraction the load the muscle is carrying at the time. 

 Measure with a pair of compasses the height of each 

 contraction in millimetres. (There is a millimetre scale 

 on the induction machine.) 



Determine the work done in gram -millimetres at each 



contraction by the formula W = - - where W = work, 



m 



w = height in mms. of the contraction, m = the magnifi- 

 cation of the contraction. The work done increases as the 

 load increases up to a certain point and then decreases. 

 On squared paper plot out (a) the curve of the height 

 of contraction with increasing load, the height in mms. 

 being the ordinates and the weight in grams the ab- 

 scissae; (b) the curve of work, the gram-millimetres of 

 work being the ordinates and the load in grams the 

 abscissae. 



The experiment may be repeated using a tetanising current for 

 one second instead of single induction shocks. 



3. Extensibility of muscle. Fix the gastrocnemius 

 of 1 in the muscle chamber. Bring the point of the 

 lever to write on the drum, and turning the drum by 

 hand trace a base line with the muscle unloaded (except 

 with the weight of the lever). With a pair of compasses 

 mark off on this a number of points -5 cm. from one 

 another. Put on a load of 20 grams attached to a long 

 hook (Fig. 18), the muscle stretches, and the lever falls, 

 recording a nearly vertical line. Move on the drum -5cm. 

 by hand, and put on another 20 grams, the lever again 

 falls but less than before. In this way record the magni- 

 fied extension of the muscle for each successive 20 grams 



