MUSCLE-NERVE PHYSIOLOGY. 533 



MUSCULAR AND NERVOUS METABOLISM. 



The question of the metabolism of muscle both in a resting and in an 

 active condition has for many years occupied the attention of physiolo- 

 gists. It cannot be said even now to be thoroughly understood. Most 

 of the facts with reference to the subject have been already mentioned. 

 We may shortly recapitulate them here: First, muscle during rest ab- 

 sorbs oxygen and gives out carbon dioxide. This has been shown by an 

 analysis of the gases of the blood going to and leaving muscles. During 

 activity, e. g., during tetanus, the same interchange of gases takes place, 

 but the quantities of the oxygen absorbed and of the carbon dioxide 

 given up are increased, and the proportion between them is altered thus: 



There is then a greater proportion of carbon dioxide produced in 

 muscle during activity than during rest. 



During rigor mortis there is also an increased production of carbon 

 dioxide. 



Second, muscle during rest produces nitrogenous crystallizable sub- 

 stances, such as kreatin, from the metabolism which is constantly going 

 on in it during life ; in addition there is in all probability sarcolactic 

 acid formed and other non-nitrogenous matters. 



During activity the nitrogenous substances, such as kreatin, undergo 

 very slight, if any, increase about the amount produced during rest 

 but the sarcolactic acid is distinctly increased; sugar (glucose) is also 

 increased, whereaa the glycogen is diminished. 



During rigor mortis the sarcolactic acid is also increased, and in ad- 

 dition myosin is formed. 



From these data it is assumed that the processes which take place in 

 resting and active muscle are somewhat different, at any rate in degree. 

 From actively contracting muscle, also, there are obtained an increased 

 amount of heat and mechanical work, more potential is converted into 

 kinetic energy. 



Many theories have been proposed to explain the facts of muscular 



