THE PHENOMENON OF CONTRACTION. 



41 



H the lift. If either Lor His equal to zero, the product, of course, 

 is zero; that is, no external work is done. 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 

 what Weber called the al^solute power of the muscle. As will be 

 seen from the above curve, it is measured by the 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 



Fig. 18.— The curve of work obtained by plotting the results shown in Fig. 1.. The 

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

 meters is represented bv 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 tound to be 

 equal to 182 gms. 



terms (Hermann), the absolute power of a muscle is the maxi- 

 mum 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. Expressed in this way, it is found that the absolute 

 power of human muscle is, size for size, much greater than that of 

 frog's muscle. For instance, the absolute power of a frog's muscle 

 of 1 square centimeter cross-area is estimated at from 0.7 kilogram 

 to 3 kilograms, while that of a human muscle of the same size is 

 estimated by Hermann at 6.24 kilograms. In general, it may be 



