94 PHYSIOLOGY OF MUSCLE AND NERVE 



material. It merely means that one kind of energy is transformed 

 into another without actually causing a change in the total amount 

 of the energy available in the universe. It is true, however, that the 

 proportion of "bound'' and ''free" energy does not remain the same; 

 in fact, the latter invariably diminishes and never increases. Like 

 all protoplasm, muscle tissue contains a store of chemical substances 

 from which it derives its necessary energy. When stimulated, certain 

 chemical processes of an explosive type are initiated in its substance 

 which cause its potential energy to be converted into kinetic energy. 

 The latter presents itself as mechanical work, heat and electricity, 

 light being excluded in this particular case. But naturally, the re- 

 lative amounts of these three forms of energy must vary considerably, 

 the production of heat greatly exceeding that of mechanical energy 

 and electricity. Individual variations are common and find their 

 origin in the character of the muscle tissue as well as in the conditions 

 under which it is made to contract. Thus we find that the muscles 

 of warm-blooded animals are able to do twice as much work per unit 

 of mass as those of cold-blooded animals and that the muscles of in- 

 sects are even more powerful than these. It has already been men- 

 tioned that red striated muscles are more powerful than pale muscles, 

 the greater effectiveness of the latter lying rather in their quickness of 

 action than in their actual strength. The liberation of energy is af- 

 fected unfavorably by fatigue, low temperatures, a high humidity of 

 the air, a poor nutritive condition of the body, and other factors. In 

 general, however, it may be said that about one-third of the total 

 amount of energy appears in the form of- mechanical energy and some- 

 what less than two-thirds in the form of heat.^ Fick,^ working with 

 excised muscles, states that under favorable conditions^ about one- 

 fourth of the total energy can be given off as mechanical work, pro- 

 vided the load used is relatively large. With smaller weights this 

 amount is proportionately diminished. 



The Work Performed by Muscle. — For ordinary purposes it suffices 

 to determine the work performed by a muscle by simply multiplying 

 the load by the height to which it has been lifted. The product is 

 then expressed in terms of milligram-meters. Thus, if a muscle raises 

 a weight of 25 grams to a height of 10 millimeters, as determined 

 by the weight of the curve recorded by it upon the kymograph, it has 

 done 250 gram-millimeters of work. In this calculation, however, 

 an allowance must be made for the magnification of the writing lever 

 in accordance with the formula: L :H : :l:h, in which L equals the 

 total length of the lever, I the length of its short arm from the axis 

 to the attachment of the muscle, H the height of each line of contrac- 

 tion and h the actual height to which the load has been lifted. The 

 work (W) is then computed in gram-millimeters in accordance with 



1 Zuntz, Pfliiger's Archiv, Ixviii, 1897, 191. 

 Ubid., xvi,.1878, 85. 



