TISSUES OF THE BODY. 285 



animals, as for instance in the frog, the nuclei lie at every depth in the 

 fibre. 



The contents enclosed in the sarkolemma, or the fleshy substance of the 

 muscle (fig. 274, 1), is of extremely complex and delicate texture. It 

 presents, but in varying degrees of distinctness, a longitudinal (c) and 

 transverse striation (d), affecting the whole thickness of the fibre. 



In many dead muscles the longitudinal marking may be observed with 

 the greatest clearness in many fibres, appearing in the form of very 

 delicate but distinct parallel lines, traversing the whole length of the 

 element. 



The distance of these from one another varies between O'OOl 1-0*0022 

 mm. In many cases the lines run continuously for a considerable dis- 

 tance, but more frequently only make their appearance at intervals in the 

 fleshy mass, and, after running a short course, disappear again. 



On transverse sections of a fibre we may frequently observe the sub- 

 stance of the contents projecting in the form of fine fibrilla3 or bands 

 (1, a), bounded by the linear marking. 



The objects, however, which we obtain by the action of certain reagents 

 on the muscle fibres are extremely peculiar, a method of treatment much 

 in use. Those which have been macerated in cold or boiled in hot water, 

 such also as have been subjected to the prolonged action of alcohol, 

 bichloride of mercury, chromic acid, and, more than all, of bichromate of 

 potash, are often seen split up 

 in the most beautiful way into 

 long fine fibres of O'OOl 1- 

 0-0022 mm. in breadth (fig. 

 276). 



Owing to this circumstance, 



it has been Supposed by many Fig. 276. A muscle fibre after the continued action of 

 ., . ,, nr 1 bichromate of potash for twenty-four hours, showing 



that the fibres 01 mUSCle are its partial resolution into fibrilhe. 



made up of fine elementary 



threads or " muscle fibrillse," as they have been named ; the muscle fibres 



are also known, on this account, as " primitive bundles." 



The theory in question has had among its defenders a number of men 

 whose opinions should have great weight. Among these we may mention 

 Schwann, Valentin, Henle, Gerlach, Koelliker, Leydig, WelcJccr, Schon. 



REMARKS. Comp. beside HenWs work, Bowman in the Phil. Transact. 1840, 

 Part 2, p. 69, and 1841, Part 1, p. 457 ; also the two articles by the same, " Muscle" 

 and "Muscular Motion," in the Cyclopaedia, vol. iii. p. 506 and 519 ; and in the 

 work edited in conjunction with Todd, vol. i. p. 150. 



165. 



The transverse striation of muscle is also subject to much variation, 

 and it is a matter of great difficulty to gain a proper conception of it, 

 owing to the minuteness of the object and the obstacles in the way of 

 correct focus. In the first place, we meet with dark, sharply defined, and 

 continuous .lines, running parallel to one another, whether in a straight or 

 undulating course. Their distance from one another likewise lies between 

 O'OOl 1 and 0'0023 mm. Again, these transverse strisB may be inter- 

 rupted, ceasing for a certain distance. The contour of the whole fibre is at 

 the same time quite smooth. In other muscle fibres, markings not so dark, 

 but much broader, are seen, regular cross-bands, so that the whole appears 

 to consist of a double system of dark and light transverse zones. Finally, 



