ADVANCED EXPERIMENTAL PHYSIOLOGY 57 



far enough, the two curve lines would ultimately cross; this means 

 that if a muscle were loaded by a weight greater than it could lift, it 



FIG. 67. Comparative extensibility of resting and contracted pastrocnemius. 

 Temp. 12* C. Magnification, 5. Figures represent actual weights in zrms. U is 

 the ' resting ' and C the ' contracted ' abscissa line. (A.P.B.) 



would during its stimulation actually lengthen (Weber's paradox). If 

 this were not so, we should, when trying to lift a load greater than the 

 muscle could move, run a great risk of rupturing our muscles. 



CHAPTER XIII. (Advanced}. 

 LOAD AND AFTER-LOAD. WORK DONE WITH INCREASING LOADS. 



MUSCLES may be loaded in two ways ; the load may be applied before 

 the muscle has begun to contract, or only after it has already begun to 

 contract ; this latter method, in order to distinguish it from the former, 

 is called ' after-loading/ Most of the muscles in the body are both 

 loaded and after-loaded; that is, they are constantly loaded by the 

 pull of their antagonists, and it is only after they have already begun 

 to shorten that the main load the weight of the limb, etc. is applied 

 to them. The deltoid, however, is an instance of a muscle constantly 

 loaded by the weight of the arm ; the ventricle of the heart, on the 

 other hand, is a muscle which is only after-loaded. 



