THE PHENOMENON OF CONTRACTION. 41 



W = L H f in which W represents the work done, L the load, and 

 H the lift. If either L or H is equal to zero the product, of course, 

 is zero; that is, no external work is done; the chemical energy 

 liberated in the contraction takes the form of heat. Second. 

 There is an optimum load for each muscle with which the greatest 

 proportion of work can be obtained. Third. When the load is just 

 sufficient to counteract the contraction of the muscle no work is 

 done, H in the above formula being zero. This amount of load 

 measures w r hat Weber called the absolute power of the muscle. 

 As will be seen from the above curve, it is measured by the 



Fig. 18. The curve of work obtained by plotting the results shown in Fig. 17. The 

 initial contraction was made with a load of 14.2 gms., and the work done in gram-milli- 

 meters is represented by the ordinate erected at this point. The maximum work was done 

 with a load of 88.6 gms., and the absolute power of this particular muscle was found to be 

 equal to 182 gms. 



weight which the muscle cannot lift and which, on the other 

 hand, cannot cause any extension of the muscle while contracting. 

 Or, in more general terms (Hermann), the absolute power of a 

 muscle is the maximum of tension which it can reach without 

 alteration of its natural length. This absolute power can be 

 measured for the muscles of different animals and for convenience 

 of comparison can then be expressed in terms of the cross-area 

 of the muscle given in square centimeters. Weber has shown 

 that the absolute power of a muscle varies with the cross-area, since 

 this depends upon the number of constituent fibers whose united 

 contraction makes the contraction of the muscle. Expressed in 



