306 



OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



Structure of the 

 ultimate fibrillai of 

 Striated Muscular 

 Fibre: a, a fibril 

 in a state of ordina- 

 ry relaxation ; 6, a 

 fibril in a state of 

 partial contraction. 



Fig. 95. fibril is in a state of relaxation, as seen at a, 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 dif- 

 ference between the two states is frequently much more 

 striking than is represented in the figure. Thus the act of 

 Muscular contraction seems to consist in a change of form in 

 the cells of the ultimate fibrillse, which must be regarded as a 

 manifestation of forces in their interior, that have been deve- 

 loped in previous acts of Nutrition ( 110) ; and it thus corre- 

 sponds very closely 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 differ- 

 ence, therefore, between the striated muscular tissue of Ani- 

 mals, and the contractile tissues of Plants, consists in the sub- 

 jection of the former to Nervous influence. The diameter of 

 the ultimate fibrillse, and the length of the component cells, 

 will of course vary according to the contracted or relaxed con- 

 dition of the fibre ; but they otherwise seem to be tolerably 

 uniform in different animals. The average diameter may be 

 stated at about l-10,000th of an inch; but it has been observed 

 as high as l-5000th, and as low as l-20,000th, even when not 

 put upon the stretch. The length of the component cells cor- 

 responds, of course, to the distance of the strise on the entire 

 fibre ; and this also has been just shown to average about 

 l-10,000th of an inch. 

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

 traction of Muscle, was for a long period that of Prevost and Dumas, who stated 

 that they were thrown into a sinuous or zigzag flexure. More recent observa- 

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

 improbability of which might have been suspected from the consideration that 

 fibres in this state of flexure could scarcely be imagined to be exerting any force 

 of traction. Prof. Owen has noticed that, in the contracted state of the very 

 transparent muscles of some Entozoa, each separate fibre, which may be seen 

 with great distinctness, presents a knot or swelling in the middle, besides being 



Am. Ed., and by Dr. Sharpey, in his new edition of Dr. Quain's "Elements of 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 published, 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 " sarcous elements" of Mr. Bowman, and re- 

 garded 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 light cells, separated by the delicate transverse line just spoken of, 

 being interposed- between each pair of dark ones ("System of Human Anat., 4th Am. Ed., 

 p. 171). 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 emi- 

 nent Microscopists in London and elsewhere (see, for example, Mr. Quekett's "Practical 

 Treatise on the Use of the Microscope," 2d edit., pi. ix., fig. 12) ; and testimony in 

 its favor has been given by some, who, before they saw the preparations which afford 

 the evidence of its truth, had entirely discredited it. (See Dr. Hassall's "Microscopic 

 Anatomy," pp. 341, 548.) 



1 See "Princ. of Phys., Gen. and Comp.," \ 138, and CHAP, xix., Am. Ed. 



