SEC. 6. THE ENERGY OF MUSCLE AND NERVE, AND THE 

 NATURE OF MUSCULAR AND NERVOUS ACTION. 



We may briefly recapitulate some of the chief results arrived at 

 in the preceding pages as follows. 



A muscular contraction itself is essentially a translocation of 

 molecules, a change of form not of bulk. We cannot say however 

 anything definite as to the nature of this translocation or as to 

 the way in which it is brought about. Though it would appear 

 that the dim doubly refractive bands increase in bulk at the 

 expense of the bright singly refractive bands, we cannot satis- 

 factorily explain the connection between the striation of a muscular 

 fibre and a muscular contraction. Nearly all rapidly contracting 

 muscles are striated, and we must suppose that the striation is 

 of some use ; but it is not essential to the carrying out of a 

 contraction, for many muscles are not striated. But whatever 

 be the exact way in which the translocation is effected, it is 

 fundamentally the result of a chemical change, of an explosive 

 decomposition of certain parts of the muscle-substance. The 

 energy which is expended in the mechanical work done by the 

 muscle has its source in the latent energy of the muscle-substance 

 set free by that explosion. Concerning the nature of that ex- 

 plosion we only know at present that it results in the production 

 of carbonic acid and in an increase of the acid reaction, and that 

 heat is set free as well as the specific muscular energy. There is 

 a general parallelism between the extent of metabolism taking 

 place and the amount of energy set free. The greater the 

 development of carbonic acid, the larger is the contraction and 

 the higher the temperature. 



It has not been possible hitherto to draw up a complete equa- 

 tion between the latent energy of the material and the two forms 

 of actual energy set free. The proportion of energy given out 

 as heat to that taking on the form of work probably varies 

 under different circumstances; and it would appear that on the 

 whole a muscle would be no more economical than a steam-engine 

 in respect to the conversion of chemical action into mechanical 



