STRIATED MUSCULAR FIBRE. 



197 



Fig. 98. 





Fragment of Muscular fibre 

 from macerated heart of Ox, 

 showing formation of striae by 

 the aggregation of fibrilte. 



Fig. 99. 



is made up of a linear aggregation of such cells.* When the fibril is in a 

 state of relaxation, as seen at or, the diameter of the cells is greatest in the 



longitudinal direction ; but when it 

 is contracted, the fibril increases in 

 diameter as it diminishes in length ; 

 so that the transverse diameter of 

 each cell equals or even exceeds the 

 longitudinal diameter, as seen at b. 

 The difference between the two 

 states is frequently much more strik- 

 ing than is represented in the figure. 

 Thus the act of Muscular contrac- 

 tion seems to consist in a change of 



form in the cells of the ultimate fibrillae, consequent upon an 

 attraction between the walls of their two extremities, or per- 

 haps between their nuclei ; and it is interesting to observe 

 how very closely it thus corresponds with the contraction of 

 certain Vegetable tissues, of which the component cells change 

 their form when irritated, and thus produce a movement ( 1). 

 The essential difference, therefore, between the striated mus- 

 cular tissue of Animals, and the contractile tissues of Plants, 

 consists in the subjection of the former to nervous influence. 

 The diameter of the ultimate fibrillae, and the length of the 

 component cells, will of course vary according to the contract- 

 ed or relaxed condition of the fibre ; but they otherwise seem 

 to be tolerably uniform in different animals. The average 

 diameter may be stated at about 1-10, 000th of an inch; but 

 it has been observed as high as l-5000th, and as low as 1- 

 20,000th, even when not put upon the stretch. The length of 

 the component cells corresponds, of course, to the distance of 

 the striae on the entire fibre ; and this also has been just shown 

 to average about 1-1 0,000th of an inch. 



231. The general opinion as to the disposition of the fibres during the con- 

 traction of Muscle, has been, until lately, that of Prevost and Dumas, who 

 stated that they were thrown into a sinuous or zig-zag flexure. Recent ob- 

 servations, however, have fully demonstrated the incorrectness of this view ; 

 the improbability of which might have been suspected from the consideration, 



* This account of the ultimate structure of Muscular Fibre was first published simulta- 

 neously (March, 1S4G), by the Author of this Treatise, in his Manual of Physiology, and by 

 Dr. Sharpey, in his new edition of Dr. Quain's Anatomy. Both of these statements, which 

 were completely independent of each other, were founded upon the examination of the very 

 beautiful preparations of Muscular Fibre, made by Mr. Lealand the Optician ; who appears 

 to have been the first to direct attention to the transverse line dividing the bright space, and 

 to the bright border edging the dark spot. A similar delineation had previously been pub- 

 lished, however, by Dr. Goodfellow (Physiological Journal, No. IV.) ; but his interpretation 

 of the appearances was altogether different; for he considered the dark spaces as the " sar- 

 cous elements" of Mr. Bowman, and regarded them as separately inclosed within partitions 

 formed by internal prolongations of the general investing Myolemma. By Mr. Erasmus 

 Wilson, again, the appearances were described as leading to the belief that two kinds of 

 cells exist in each fibrilla, a dark and a light ; a pair of b'ght cells, separated by the delicate 

 transverse line just spoken of, being interposed between each pair of dark ones [System of 

 Anatomy, 3d Am. Edit., p. 183]. The bright edging to the dark spots was overlooked by 

 him. The view taken by Dr. Sharpey and the Author has the entire concurrence of several 

 of the most eminent Microscopists in London and elsewhere ; and it is confirmed by the 

 remarkable similarity between the aspect of the Muscular fibrilla, and that of a minute Con- 

 i'erva, seen under the same magnifying power, the cellular constitution of the latter being 

 indubitable. 



17* 



Structure of the 

 ultimate fibrillse of 

 striated muscular 

 fibre : a, a fibril 

 in a state of ordi- 

 nary relaxation ; 

 b, a fibril in a state 

 of partial contrac- 

 tion. 



