78 HUMAN PHYSIOLOGY 



precede contraction but comes in its wake. Yet we 

 believe as firmly as ever in the conservation of energy 

 and that there is a correspondence between the work 

 done and the fuel consumed. Are there any analogies 

 which can be employed now that the steam engine has 

 failed us? We shall find that there are. 



If oxidation follows muscular movement we must 

 -conclude that its purpose is to make ready for subsequent 

 action. Some of the energy liberated must become 

 latent in some way and so be held ready for release either 

 shortly or after some time. This is not an unfamiliar 

 condition in the field of mechanics. In the pile driver, 

 for instance, the engine works to lift the weight which 

 may then be hung at the top of the guides and let fall 

 whenever desired. The oxidation has taken place after 

 the fall of the weight upon the pile. To be sure, it has 

 to precede the next descent, but an indefinite time may 

 pass before this takes place. So, in the case of the air 

 brake, preparation is made by pumping air into con- 

 tainers, but this may be done long before the occasion 

 for using the brake. When it is set there is no call for 

 the sudden burning of fuel, but directly after the train 

 has been stopped we hear the pump at work, preparing 

 the system for later service. 



The muscle may also be compared with an electric 

 power house in which there are storage batteries. The 

 engines are run when convenient to drive the dynamos 

 and charge the batteries. These will give back energy 

 at any time in connection' with chemical changes in their 

 cells. It will be found that this is quite closely analogous 

 to the case of the muscle. The simplest image that we 

 can select is that of the\bent bow, drawn back and held 

 in readiness for letting go. We must remember that 

 when a muscle is in tetanus the oxidation that follows 

 each momentary act of contraction is so closely followed 

 by another movement that the order of the processes is 

 obscured. The fibers of such a muscle are like a legion 

 of archers, discharging arrows as fast as they can handle 



