THE PRODUCTION OF ENERGY IN MUSCLE 95 



the formula : W = wh, in which w signifies the weight and h the height 

 to which it has been raised. 



From these results it may be gathered first of all that the product 

 must become zero if no weight at all is attached to the muscle. When 

 not loaded, therefore, a muscle does practically no external work and 

 the chemical changes occurring during its contraction are almost 

 wholly converted into heat and a small amount of electricity. The 

 word "practically" is inserted here, because a muscle even when not 

 carrying a weight, must overcome its own resistance which, to be sure, 

 is so slight that nearly all of its energy can appear as heat. This 

 modification could of course be rendered superfluous by adjusting the 

 muscle in a horizontal manner and immersing it in oil to overcome this 

 friction as much as possible. In the second place, it is also evident that 

 the product must become zero if H equals zero, and even when the 

 muscle is loaded with so heavy a weight that it is quite unable to lift it. 

 As in the preceding case, most of the energy liberated is then turned 

 into heat. 



Attention should also be called to the fact that a muscle which 

 merely contracts and relaxes, raising and lowering a weight, really 

 furnishes no energy to its surroundings, because it develops no kinetic 

 energy at this time. In order to accomplish actual work, it would be 

 necessary for it to produce certain changes. This end it could easily 

 accomplish by raising a weight to a definite height and permitting it 

 to fall to the surface of the earth. The potential energy stored in it 

 would then be converted into kinetic energy. 



We have previously seen that a muscle, when properly counter- 

 poised and made to react successively against a steadily increasing 

 load, exhibits a gradual decrease in the height of its contractions. 

 Eventually a weight will be found which it is quite unable to lift. At 

 this time, therefore, the load counteracts the contractile power of the 

 muscle and no mechanical energy is liberated. This weight which 

 merely places the muscle under a maximal degree of tension and does 

 not permit it to change its length, has been designated by Weber as the 

 absolute power of the muscle. Moreover, since this power is propor- 

 tional to the cross-section of the muscle, we are in a position to obtain 

 a standard by simply determining the absolute force for one square 

 centimeter of muscle substance. This value, to be sure, differs in 

 different muscles, because such factors as the character of the myo- 

 plasm and the number and arrangement of the muscle fibers, give rise 

 to individual variations. For frog's muscle, values ranging between 

 0.7 and 3.0 kilograms per centimeter of cross-section have been found. 

 The experiments upon human muscles have been made during volun- 

 tary contractions and not during artificial tetanization, while the cross- 

 sections of the muscles employed for these tests have been determined 

 upon dead subjects of the same physique as the person experimented 

 upon. Hermann 1 gives the average absolute force of human muscle 

 » Pfltiger's Archiv, Ixxiii, 1898, 429. 



