494 MUSCLE-NERVE PHYSIOLOGY 



and the intestine be tied at the opposite end, and filled with water, the water 

 will in a few hours rise to a considerable height in the tube, owing to the con- 

 traction of the intestinal walls. It is still better shown in the arteries, of 

 which all that have muscular coats contract after death, and thus present the 

 roundness and cord-like feel of the arteries of a limb lately removed or those 

 of a body recently dead. Subsequently they relax, as do all the other mus- 

 cles, and feel lax and flabby and lie as if flattened and with their walls 

 nearly in contact. 



Muscular Metabolism During Contraction. The question of the 

 metabolism of muscle both in a resting and in an active condition has for 

 many years occupied the attention of physiologists. 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 absorbs 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 inter- 

 change 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: 



Venous blood. 



O 2 , less than in arterial 

 blood. 



Co 2 , more than in arterial 

 blood 



Of resting muscle 9 per cent. 



Of active muscle . 



12.26 per cent. 



6.71 per cent. 



10.79 per cent. 



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 creatin, from the metabolism which is constantly going on 

 in it during life; in addition there are formed, in all probability, sarcolactic 

 acid and other non-nitrogenous matters. 



During activity the nitrogenous substances, such as creatin, undergo 

 very slight, if any, increase above the amount produced during rest but 

 the sarcolactic acid is distinctly increased. The glycogen stored in the 

 muscle is gradually converted into dextrose and the latter oxidized to 

 furnish the energy developed in the contraction. 



