54 TEXT-BOOK OF PHYSIOLOGY 



The Blood-supply. Muscles in the physiologic condition require for 

 the maintenance of their activity a large amount of nutritive material. This 

 is obtained directly from the lymph and indirectly from the blood furnished 

 by the blood-vessels. The vascular supply to the muscles is very great and 

 the disposition of the capillary vessels with reference to the muscle-fiber is 

 very characteristic. The arterial vessels, after entering the muscle, are 

 supported by the peri-mysium; in this situation they give off short transverse 

 branches, which immediately break up into a capillary network of rectangu- 

 lar shape within which the muscle-fibers are contained. 



The muscle-fiber, in intimate relation with the capillary, is bathed with 

 lymph derived from it. Its contractile substance, how- 

 ever, is separated from the lymph by its own investing 

 membrane, through which all interchange of nutritive and 

 cd waste material must take place. 



The nutritive material passes through the capillary 

 wall into the lymph-space, then through the sarcolemma 

 ,, |; n H ;| n | into the interior of the fiber, where it comes into relation 

 with the living muscle material. The waste products 

 arising in the muscle as a result of nutritive changes pass 

 in the reverse direction first into the lymph and then into 

 the blood, by which they are carried away to eliminating 

 organs. Lymphatics are present in muscle, but confined 

 to the connective tissue, in the spaces of which they take 

 their origin. 



The Nerve-supply. The nerves which carry the 

 stimuli to a muscle enter near its middle point. Many 

 of the fibers pass directly to the muscle-fibers with which 

 they are connected; others are distributed to blood-vessels. 

 Every muscle-fiber is supplied with a special nerve-fiber 

 except in those instances where the nerve-trunks entering 

 a muscle do not contain as many fibers as the muscle. In 

 GRAM IG 'op 17 MuscLE sucn cases the nerve-fibers divide near their termination 

 STRIATIONS. (Modi- until the number of branches equals the number of muscle- 

 fied from "Swnr's fibers. The individual muscle-fiber is penetrated near 

 SriUa^coiLuts Th of its cent er by the nerve where it terminates; the ends 

 alternate dark bands, being practically free from nerve influence. The stimulus 

 rf.6.,andlight^ban^, tnat comes to the muscle-fiber acts primarily upon its 

 by Krause's "mem- center, the effect of which then travels in both directions 

 brane, m. ; a similar to the ends. The manner in which the nerve-fibers termi- 



SeduSibMdiSSS nate in muscle wil1 be more full 7 described in connection 

 ing to Heidenhain. with the histology of the nerve-tissue. 



CHEMIC COMPOSITION OF MUSCLE 



The chemic composition of living muscle is but imperfectly understood 

 owing to the fact that shortly after death some of its constituents undergo a 

 spontaneous coagulation and for the reason that the methods employed for 

 analysis also tend to alter its composition. To human muscle, the following 

 average percentage composition has been given : 



