THE MUSCULAR SYSTEM. 265 



up, whilst when the circuit is broken they elongate themselves as rapidly 

 as they contracted, and present zigzag flexures, when the muscle is lying 

 free, but not when it is stretched by small weights attached to it by 

 threads. From this it is evident, that if zigzag flexures take place 

 during life, which is not yet known to occur, they can only arise when 

 muscles in the quiescent condition are not in a state of tension ; as, for 

 instance, in the case of a flexor muscle, which has come into a state of 

 rest after it has produced its full effect upon the limb. The sarcolemma 

 is readily seen in the muscles of Amphibia and Fishes, especially in 

 specimens preserved in spirit, in which it frequently, but for the most 

 part in places, appears at a distance from the fibrils. In the higher 

 animals and in man, it is occasionally seen when the fasciculi are teased 

 out ; and also in macerated and boiled muscles, and on the addition of 

 acetic acid or alkalies. For this purpose I would especially recommend 

 caustic soda, which in many cases renders the contents of the muscular 

 tubules so fluid, that they escape in a continuous stream together with 

 the nuclei, when the sheaths come very clearly into view. In no case, 

 however, is the sarcolemma, in man, more beautifully exhibited than it is 

 in softened, atrophied muscles which have undergone fatty or other de- 

 generations ; and, in fact, the greater the degree of degeneration, the 

 more distinctly is this structure exhibited. The muscular fibrils, in fresh 

 muscles, are constantly visible only in a transverse section, and in the 

 thoracic muscles of insects, elsewhere it is true they are occasionally 

 seen, but more by chance than otherwise. They are easily isolated 

 artificially in preparations preserved in spirit, particularly in the peren- 

 nibranchiate Reptiles (Siredon, Proteus, &c.), by treatment with chromic 

 acid (Hannover), by maceration for from 8 to 21 days, at a temperature 

 of 18 R. in water, to which, for the prevention of putrefaction, some 

 corrosive sublimate has been added (Schwann) ; maceration also in the 

 fluids of the mouth (Henle) allows of their being readily exhibited ; 

 whilst, according to Frerichs (Wagner, " Handworterb.," III. I. p. 814), 

 in the stomach, the fasciculi break up into Bowman's discs. The nuclei 

 of the fasciculi are best studied under the application of acetic acid ; by 

 soda (vide supra) they may be isolated, and by potassa be made to swell 

 considerably (Donders). On the subject of the effect of various reagents 

 on the elementary tissues of muscle, the treatises of Donders (Holland. 

 "Beitrage") and Paulsen (" Observ. michrochem.," Dorpat, 1849) may 

 be consulted. The vessels of muscle are studied in fresh, thin muscles, 

 and in injected preparations; the nerves in the smallest human muscles, 

 in the muscles of the smaller Mammalia, in the cutaneous muscle on the 

 thorax of the Frog, with or without the addition of soda. The perimysium, 

 and the form and position of the muscular fibres, are very well shown 

 in transverse sections of half-dried muscles; and the same observation 

 holds good with respect to the elementary tissues of the tendons. The 



