174 



THE MUSCLE CELLS 



acid as mentioned in the preceding paragraph has a positive 

 temperature coefficient. The building up of lactic acid into a 

 complex is accelerated by increase of temperature just like any 

 other chemical reaction. 



Rest. During complete inactivity, energy is used for maintain- 

 ing the muscle in a state of preparedness for action, just as a nation 

 has to spend money maintaining an army in peace time, so the 

 muscle cell must always be ready for action. This is the fifth phase 

 of the muscular cycle — erroneously termed rest. This stage is 

 anything but restful. Just as in peace time the co-ordinating and 

 integrating machine of Empire, the Cabinet, keeps our standing 

 army in a high state of efficiency, so the nervous system constantly 

 sends impulses to the muscles, keeping them ready for instant 

 action. This state of resting readiness may be called the tone of 

 muscle, and is, as indicated above, regulated in part by the nervous 

 system (q.v.). During rest, energy is expended which if sub- 

 tracted from the total energy expended during restitution would 

 raise the efficiency of that phase by about 4 per cent. 



TABLE XXVIII 

 Oxygen used by Cat's Gastrocnemius M. (Verzar, 1912) 



Function of Lactic Acid. Lactic acid liberation is the pivot 

 round which all the modern theories of muscular contraction 

 revolve. Five such hypotheses deserve mention. 



(1) Surface Tension Theory. Lactic acid lowers the surface 

 tension of water and so might alter the interfacial tension of oval 

 eleinents and their plasma. 



A glance at Fig. 42 may make it clear how surface energy may 

 be made to do work. 



