CHEMICAL CHANGES IN CONTRACTING MUSCLE 451 



muscular tissue, but to the increased tension to which the fibers, as well as their 

 tendons and other tissues, are subjected from the resistance ordinarily opposed 

 to their contraction. When no resistance is offered, as when a muscle is cut 

 off from its tendon, not only is no hardness perceived during contraction, but 

 the muscular tissue is even softer and more extensible than in its ordinary 

 uncontracted state. During contraction in each fiber it is said that the aniso- 

 tropous or doubly refractive elements become less refractive and the singly 

 refractive more so, figure 321. 



Chemical Changes in Contracting Muscle, i. The reaction of the 

 muscle, which is normally alkaline or neutral, becomes decidedly acid during 

 contraction, from the development of sarcolactic acid. 2. The muscle gives 

 out carbon dioxide gas and takes up oxygen. The amount of the carbon dioxide 

 given out does not appear to be entirely dependent upon the oxygen taken in, 

 and so doubtless in part arises from some other source. Muscle contracts in 



FIG. 323. Diagram of Du Bois Raymond's Non-polarizable Electrodes, a, Glass tube filled 

 with a saturated solution of zinc sulphate, in the end, c, of which is china clay drawn out to a 

 point; in the solution a well-amalgamated zinc rod is immersed and connected, by means of the 

 wire which passes through a, with the galvanometer. The remainder of the apparatus is simply 

 for convenience of application. The muscle and the end of the second electrode are to the right 

 of the figure. 



an atmosphere of hydrogen, showing that oxygen is present in fixed combina- 

 tion. A muscle, however, contracts for a longer time in an atmosphere of 

 oxygen. 3. Certain imperfectly understood chemical changes occur, in all 

 probability connected with i and 2, in which glycogen is diminished, and 

 glucose and muscle sugar, inosite, appear. The nitrogenous extractives are 

 also increased. 



Electrical Changes in Contracting Muscle. Resting muscles un- 

 injured in the body have a uniform potential, are isoelectric. But when 

 removed from the body they are more or less injured and, therefore, show 

 differences of electrical potential between different points on the muscle, 

 called currents of injury or demarcation currents. 



