646 A MANUAL OF PHYSIOLOGY 



The work done by a muscle in raising a weight is equal to the 

 product of the weight by the height to which it is raised. Beginning 

 with no load at all, it is found that the weight can be increased up to 



FIG. 232. INFLUENCE OF LOAD ON THE FORM OF THE MUSCLE CURVE. 



i, curve taken with unloaded lever ; 2, 3, 4, weight successively increased ; 

 5, abscissa line ; time trace, T ^ T second (reduced). 



a certain limit without diminishing the height of the contraction ; 

 perhaps the height may even increase. Up to this limit, then, the 

 work evidently increases with the load. If the weight is made still 

 greater, the contraction becomes less and less, but up to another 



FIG. 233. INFLUENCE OF TEMPERATURE ON THE STRIATED MUSCLE CURVE. 



2, air temperature j i, 25 30 C. ; 3, 7 10 C. ; 4, ice in contact with muscle. 

 The fifth curve was taken at a little above air temperature. 



limit the increase of weight more than compensates for the diminu- 

 tion of ' lift,' and the work still increases. Beyond this, further 

 increase of weight can no longer make up for the lessening of the 



