112 



MUSCULAB TISSUE 



the essential contractile element, the sarcoplasm serving largely as a nutri- 

 tive substance. However, it should also be mentioned that it has been held 

 that the sarcoplasm may be the essential contractile substance. 



Meigs questions the pertinency of Engelmann's 'artificial muscle' in 

 his catgut experiment, and the validity of the suggested hypothesis of con- 

 traction as a thermodyiiamic phenomenon. He regards contraction as 

 the result of a rise in osmotic pressure and the consequent imbibition 

 of fluid caused by the breaking down of larger into smaller molecules 

 within the sarcostyles. According to Roaf (Proc. Roy. Soc., Series B. 88, 

 1914) contraction can be explained on the hypothesis that lactic acid is 

 set free, and that this combines with certain proteins to form salts, with 

 a consequent rise of osmotic pressure. 



We must now consider the muscle as a whole. For this purpose 

 we may select any well-known muscle, for example, the biceps. A muscle 



as seen in transverse section 

 is enveloped in a moderately 

 dense, fibro-elastic mem- 

 brane, the epimysium (ex- 

 ternal perimysium) ; this 

 gives off septa which sep- 

 arate the muscle into a 

 larger or smaller number of 

 bundles, depending upon its 

 size, each bundle, or fascicu- 

 lus, being again separately 

 closely enveloped in a fibro- 

 elastic covering, the peri- 



FIG. 127. STRIATED MUSCLE FIBERS 

 DOG. 



The blood-vessels have been filled by injection 

 with a gelatinous mass and are represented in 

 black. One whole fasciculus and one fiber from 

 an adjacent fasciculus have been included, a, 

 perimysium; b, endomysium; c, a large vein seen 

 in transection. The section was not stained. 

 X 53. 



mysium (internal perimy- 

 sium). Each fasciculus is, 

 moreover, again subdivided 



into larger and smaller collections of muscle fibers, each bundle imper- 

 fectly separated from its fellows by septa from the perimysium, the endo- 

 mysium. The ultimate subdivisions of the endomysium completely en- 

 velop each fiber and blend with the sarcolemma. This brings us to an 

 individual fiber. Each fiber is enclosed in a sarcolemma. The myofibrillae 

 are collected into larger and smaller bundles, Ko'Uiker's columns, sepa- 

 rated from each other by semifluid, granular sarcoplasm; these collec- 

 tions in cross section are known as the areas of Cohnheim. They repre- 

 sent the definitive division products of the original group of fibrils (Heid- 

 euhain). The ultimate histologic units are the myofibrilla or sarcostyles. 



