154 THE ENERGY OF MUSCLE AND NERVE. [BOOK i. 



gives rise to the myosin clot, the carbonic acid, and lactic acid or 

 other acid-producing substances of rigor mortis, is the same stuff 

 which gives rise to the carbonic acid and lactic acid or other acid- 

 producing substances of a contraction. The difference between the 

 two seems to be that in the contraction the nitrogenous product of 

 the decomposition of the inogen does not appear as solid myosin 

 but assumes the form of some soluble proteid. The important 

 fact concerning the two acts, rigor mortis and contraction, is that, 

 while the great non-nitrogenous product of the decomposition of the 

 inogen, viz. carbonic acid, is simple waste matter containing no 

 energy, fit only to be cast out of the body at once (and the same 

 is nearly true of the other non-nitrogenous product, lactic acid), 

 the nitrogenous product being a proteid is still a body containing 

 much energy, which in the case of the living muscle may after the 

 contraction be utilized by the muscle itself or, being carried away 

 into the blood-stream, by some other parts of the body. 



But if this view be correct the ordinary metabolism going on 

 while the muscle is at rest must differ in kind as well as, and per- 

 haps more than, in degree from the metabolism of contraction ; for 

 the former as we have just said is essentially a nitrogenous meta- 

 bolism largely contributing to the nitrogenous waste of the body at 

 large. 



Whether in the muscle at rest this nitrogenous metabolism is 

 confined to that part of the muscle in which the inogen is lodged 

 and does not involve the inogen itself, or whether the inogen as well 

 as the rest of the fibre undergoes metabolism when the muscle is at 

 rest, going off in puffs, so to speak, instead of in a large explosion, 

 its nitrogenous factors being at the same time involved in the 

 change, are questions which we cannot at present settle. 



88. While in muscle the chemical events are so prominent that 

 we cannot help considering a muscular contraction to be essentially a 

 chemical process, with electrical changes as attendant phenomena 

 only, the case is different with nerves. Here the electrical pheno- 

 mena completely overshadow the chemical. Our knowledge of the 

 chemistry of nerves is at present of the scantiest, and the little we 

 know as to the chemical changes of nervous substance is gained by 

 the study of the central nervous organs rather than of the nerves. 

 We find that the irritability of the former is closely dependent on 

 an adequate supply of oxygen, and we may infer from this that in 

 nervous as in muscular substance a metabolism, of in the main an 

 oxidative character, is the real cause of the development of energy; 

 and the axis-cylinder, which as we have seen is most probably the 

 active element of a nerve-fibre, undoubtedly resembles in many of its 

 chemical features the substance of a muscular fibre. But we have as 

 yet no satisfactory experimental evidence that the passage of a 

 nervous impulse along a nerve is the result, like the contraction of a 

 muscular fibre, of chemical changes, and like it accompanied by an 

 evolution of heat. On the other hand, the electric phenomena are so 



