MUSCLE. 



grow dark. The addition of a little acid, how- 

 ever, swells the fibre, obliterates the cross lines, 

 and brings the corpuscles into view, not only 

 at this early period, but at every subsequent 

 one, even to old age. In insects, the nuclei 

 in the earliest stage are a single or double 

 series in the axis of the fibre, and in the per- 

 fect fibre they hold the same position (Jigs. 

 292 and 293, c). In the Vertebrate classes 

 they have a like correspondence, being scat- 

 tered equally throughout the mass, in both 

 foetal and adult states. Where the fibre is 

 small, however, they usually abound more 

 towards the surface. They are oval and flat, 

 and of so little substance, that though many 

 times larger than the primitive particles, and 

 lying amongst them, they do not interfere 

 with their mutual apposition and union. 

 These corpuscles are frequently the cause of 

 irregular dark longitudinal streaks, seen in the 

 fibre by transmitted light. They usually contain 

 some central granules or nucleoli (Jig. 295). 

 It is doubtful whether the corpuscles or nuclei 

 originally present remain through life, or whe- 

 ther successive crops advance and decay during 

 the progress of growth and nutrition. But it 

 is certain, that, as development proceeds, fresh 

 corpuscles are deposited, since their absolute 

 number is far greater in the adult than in the 

 foetus, while their number, relatively to the 

 bulk of the fibre, at these two epochs, remains 

 nearly the same. 



7. Of the sarcolemma, or tunic of the ele- 

 mentary fibre. This is a simple transparent 

 homogeneous membrane of extreme tenuity, 

 but very tough and elastic, which, in the form 



the swollen mass emerges at its broken and 

 open end : but, if this is not effected with suf- 

 ficient celerity, the sarcolemma may give way 

 at different points, being burst by the mass, 

 which thus forms herniae. Such protruding 

 masses being unequallv stretched have their 

 transverse and longitudinal lines distorted from 

 their true direction and thrown into very ele- 

 gant curves (Jig. 295). Again, if a fibre still 



Fig. 295. 



Part of an elementary fibre from the human sub- 

 ject, treated with phosphoric acid. 



a, point at which the sarcolemma is burst. 



b, hernia of the sarcons mass, with distortion 

 of the longitudinal and transverse lines. 



c, a smaller hernia. 



Corpuscles are seen scattered throughout the mass, 

 and some detached ones, d, are represented below. Their 



of a perfect tube, invests every elementary fibre, average diameter is one-thousandth of an English inch. 



adheres to its surface, and isolates it from sur- 

 rounding parts. It is universally present in vo- 

 luntary muscles, and may be demonstrated in a 

 variety of ways. When the fibres have been im- 

 mersed in alcohol, which causes them to shrink, 

 it is often seen wrinkled on their surface ; or 

 when they are cracked or broken across, it fre- 

 quently remains entire and connects the severed 

 fragments (fig. 294). This method of showing 



Fig. 294. 



Foments 



Sarcolemma. b, b, opposite fragments of the fibre. 



it is best followed in the case of the large and 

 brittle fibres of the Skate ; or, it may be seen 



retaining its irritability, be immersed in water, 

 this fluid, on being absorbed, excites contrac- 

 tion, by which it is immediately expelled from 

 among the primitive particles. When thus 

 forced out it usually collects between the 

 fibre and its sheath, raising the lattefin the 

 form of bullae (figs. 301 and 302, and Art. 

 MUSCULAR MOTION). The progress of this in- 

 teresting phenomenon evinces the adhesion that 

 exists between the fibre and its sheath. The 

 bullae immediately subside, by the 

 transudation of their fluid, when the 

 part is placed in thick syrup. I once 

 met with a singular demonstration of 

 the existence and properties of the sar- 

 colemma, in finding it filled with nu- 

 merous trichina (fig. 296), which had 

 taken the place of the contractile ma- 

 terial, the sheath preserving all its cha- 

 held to ether racteristic beauty and transparency.* 

 ,' I discovered this remarkable mem- 



brane in Insects, Crustacea, and all 

 the tribes of Vertebrata, in 1839, not 

 knowing that Professor Schwann had pre- 

 viously described it in connection with the de- 



cut across in a general transverse section of a velopment of muscle in Insects and Fish.f 



dried muscle (fig. 290). When the texture He believes it to be a persistent portion of 



of the fibre is destroyed by maceration, the the membrane of the original cells of de 

 broken mass is sometimes retained by the 



sheath, which thus becomes visible. When ^uct. loc. cit. p. 480, pi. xvii, figs. 41-5. 



the fibre swells by acid, this tunic resists, and f Mikros. Untrrsurh. p. 165. 



