GENERAL PHYSIOLOGY OF MUSCULAR TISSUE. 51 



Transmission of the Contraction Wave. Normally, when a muscle is 

 stimulated by the nerve impulse, the shortening and thickening of the fibers 

 begin at the end organ and travel in opposite directions to the ends of the 

 muscle. This change propagates itself in a wave-like manner, and has been 

 termed the contraction wave. If a stimulus be applied directly to the end of 

 a long muscle, the contraction wave passes along its entire length to the 

 opposite extremity, in virtue of the conductivity of muscular tissue. The 

 rapidity of the propagation varies in different animals in the frog, from 

 three to four meters a second, in man, from ten to thirteen meters. The 

 length of the wave varies from 200 to 400 millimeters. 



Graphic Record of a Muscle Contraction. The changes in the form of 

 a muscle during contraction and relaxation have been carefully studied by 

 recording the muscle movement by means of an attached lever, the end of 

 which is allowed to rest upon a moving surface. The time relations of all 

 phases of the muscular movement are obtained by placing beneath the lever 

 a pen attached to an electro-magnet thrown into action by a tuning-fork 

 vibrating in hundredths of a second. A marking lever records simultaneously 

 the moment of stimulation. 



Single Contraction. When a single electric induction shock is applied 

 to a nerve close to the muscle, the latter undergoes a quick pulsation, speedily 

 returning to its former condition. As shown by the muscle curve (see Fig. 4) 



FIG. 4. MUSCLE CURVE PRODUCED BY A SINGLE INDUCTION SHOCK APPLIED TO 



A MUSCLE. (Landois.) 



a-f . Abscissa, a-c. Ordinate. a-b. Period of latent stimulation, b-d. Period o 

 increasing energy, d-e. Period of decreasing energy, e-f. Elastic after-vibrations 



there is between the moment of stimulation and the beginning of the contrac- 

 tion a short but measurable period, known as the latent period, during which 

 certain chemic changes are taking place preparatory to the exhibition of the 

 muscle movement. Even when the electric stimulus is applied directly to 

 the muscle, a latent period, though shorter, is observable. The duration of 

 this period in the skeletal muscles of the frog has been estimated at o.oi of 

 a second; but it has been shown by the employment of more accurate methods 

 and the elimination of various external influences to be much less not more 

 than 0.0033 to 0.0025 f a second. 



