MUSCULAR CONTRACTION 425 



During contraction certain important changes are observed in the mus- 

 cles themselves : They change in form, consistence, and to a certain 

 extent in their constitution ; the different periods of their stimulation, 

 contraction and relaxation are positive and well marked ; their nutrition 

 is for the time modified ; they develop electric currents ; and in short, 

 they present a number of general phenomena, distinct from the results 

 of their action, that are more or less important. 



The most prominent of the phenomena accompanying muscular 

 action are shortening and hardening of the fibres. It is necessary only 

 to observe the action of any well-developed muscle to appreciate these 

 changes. The active shortening is shown by the approximation of the 

 points of attachment, and the hardening is sufficiently palpable. The 

 latter phenomenon is marked in proportion to the development of 

 the true muscular tissue and its freedom from inert matter, such as fat. 

 Notwithstanding the marked and constant changes in the form and 

 consistence of the muscles during contraction, their actual volume under- 

 goes modifications so slight that they may be disregarded. 



Changes in the Form of the Muscular Fibres during Contraction. 

 An essential experimental condition in the study of the mechanism of 

 muscular action is to imitate, in a muscle or a part of a muscle that can 

 be subjected to direct observation, the force that naturally excites it to 

 contraction. The application of electricity to the nerve is the most 

 convenient method that can be employed for this purpose. In this 

 way a single contraction may be produced, or by employing a rapid 

 succession of impulses, so-called tetanic action may be excited. While 

 the electric current is not identical with nerve-impulses, it is the best 

 substitute that can be used in experiments on muscular contractility, and 

 it has the advantage of affecting but little the physical and chemical 

 integrity of the nervous and muscular tissues-. 



A description of the electric current and its generation, with the 

 different forms of electric apparatus, belongs properly to physics and 

 would be out of place in a text-book on physiology. It is sufficient to 

 say that apparatus has been devised for the study of muscular contrac- 

 tion that enables experimenters to stimulate muscles either directly, 

 or indirectly through excitation of motor nerves. The contractions pro- 

 duced by exciting a muscle through stimulation of its motor nerve most 

 nearly resemble normal muscular action. 



In the study of the phenomena of muscular contraction, a so-called 

 nerve-muscle preparation is most useful. This is simply the leg of a 

 frog detached from an animal just killed, the skin removed, and the 

 sciatic nerve remaining attached to the muscles. With this preparation, 

 a stimulus may be applied either to the nerve or directly to the muscle. 



