THE DEMONSTRATION OF MUSCLE CURRENTS 481 



fiber loses in length, it gains in thickness. The contraction is a change of 

 form, not of size; it is, therefore, not attended with any diminution in bulk 

 from condensation of the tissue. This has been proved for entire muscles, 

 by making a mass of muscles, or many fibers together, contract in a vessel 

 full of water, with which a fine, perpendicular, graduated tube communi- 

 cates. Any diminution of the bulk of the contracting muscle would be 

 attended by a fall of fluid in the tube, but when the experiment is carefully 

 performed, the level of the'water in the tube remains the same, whether the 

 muscle be contracted or not. 



In thus shortening, muscles appear to swell up, becoming rounder, more 

 prominent, harder, and apparently tougher. But this hardness of muscle in 

 the state of contraction is not due to increased firmness or condensation of the 

 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 anisotropous or doubly refractive elements become less refract- 

 ive 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 an atmosphere of hydrogen, showing that oxygen is present in 

 fixed combination. 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 con- 

 verted into dextrose and the latter oxidized. 



Electrical Changes in Contracting Muscle. Resting muscles un- 

 injured in the body have a uniform potential, i.e., 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. 



The Demonstration of Muscle Currents. The demonstration of electrical 

 currents in muscle requires a galvanometer and non-polarizing electrodes. A 

 muscle prism is insulated, and a pair of non-polarizable electrodes connected 

 with a very delicate galvanometer, figure 322, are applied to various points 

 of the prism ; and by a deflection of the needle to a greater or less extent in one 

 direction or another, the strength and direction of the currents in the piece of 

 muscle can be determined. It is necessary to use non-polarizable and not 

 metallic electrodes in this experiment, as otherwise there is no certainty that 



