CHEMISTRY OF WORKING MUSCLE, 431 



the oxygen a muscle uses in contracting is not taken up by 

 it at the time it is used, since a muscle containing no oxy- 

 gen will still contract in a vacuum and form carbon dioxide. 

 It is probable that the chemical phenomena occurring in con- 

 traction and rigor are essentially the same; the death stiffen- 

 ing results when they occur to an extreme degree. Pro- 

 visionally one may explain the facts as follows A muscle in 

 the Body takes up from the blood, oxygen, proteids, and 

 non-nitrogenous (carbohydrate or futty) substances. These 

 it builds up into a highly complex and very unstable com- 

 pound, comparable, for example, to nitre-glycerine. When 

 the muscle is stimulated this falls down into simpler sub- 

 stances in which stronger affinities are satisfied; among 

 these are carbon dioxide arid sarcolactic acid and a proteid 

 (myosin). The energy liberated is thus independent of 

 any simultaneous taking up of oxygen; the amount possible 

 depends only on how much of the decomposable body existed 

 in the muscle. Under natural conditions the carbon diox- 

 ide is carried oil in the blood and perhaps the sarcolactic 

 acid also, the latter to be elsewhere oxidized further to 

 form water and more carbon dioxide. The myosin remains 

 in the muscle-fibre and is combined with more oxygen, 

 and with compounds of carbon and hydrogen taken from 

 the blood, and built up into the unstable energy-yielding 

 body again; none of it, under ordinary circumstances, 

 leaves the muscle. If, however, the blood-supply be defi- 

 cient, the myosin clots (p. 125) before this restitution takes 

 place and it cannot then be rebuilt; and in excessive work 

 the same thing partially occurs, the decomposition occur- 

 ring faster than the recomposition; the clotted myosin is 

 then broken up into simpler bodies and yields a certain 

 increase of the urea excreted. In rigor mortis all the myosin 

 passes into the clotted state and causes the rigidity. A 

 working muscle takes up more oxygen from the blood than a 

 resting one, as is shown by a comparison of the gases of its 

 venous blood in the two cases; this oxygen assumption is 

 not necessarily proportionate to the carbon-dioxide elimina- 

 tion at the same time; for the latter depends on the break- 

 ing down of a body already accumulated in the muscle dur- 



