MUSCLES OF ORGANIC LIFE. 



279 



traces of fibrillse can be observed in it. This tube takes its origin, like the 

 ducts of Plants, in cells laid end to end, the cavities of which coalesce, by the 

 disappearance of the partitions, at a subsequent period ; and the nuclei of 

 these original cells may be distinctly seen, for some time after the appearance 

 of the striae, which indicate the formation of the fibrillae in their interior. In 

 an early stage of the development of the fibres, indeed, these bodies project 

 considerably from their sides : in this respect as well as in others, there is a 

 close correspondence between the temporary character of the Muscular fibre 

 of Animal life, and the permanent condition of that of Organic life. In the 

 fully-formed muscle of Animal life, they are not perceptible, except when a 

 peculiar method has been adopted for bringing them into view. This method 

 consists in treating the fibre with weak acids, which render the nuclei more 

 opaque, whilst the surrounding structure becomes more transparent. They 

 are usually numerous in proportion to the size of the fibre ; when the fibre is 

 small, as in Birds or Mammalia, they lie at or near its surface ; but in those of 

 greater bulk, as in Fishes and Reptiles, they are intermingled with the fibrillae 

 through the whole thickness of the fibre, and are brought into view by a 

 transverse section. It would seem probable that these bodies are continually 

 exercising their functions, that of giving origin to new cells, and thence to 

 new muscular tissue ; since their amount is far greater in the adult than in 

 the fetus, their number relatively to the bulk of the fasciculi (which is in the 

 fetus about one-third of that of the adult) being nearly the same at the two 

 periods. In the Larvae of several Insects, perfect and imperfect fibres may 

 often be found lying side by side. 



III. Muscles of Organic Life. 



375. The Muscular fibre of Organic life is very different from that which 

 has been thus fully described. It consists of a series of tubes which do not 

 present transverse striae, and in which the longitudinal striae are very faint ; 

 these tubes are usually much flattened, and cannot be shown to contain dis- 

 tinct fibrillae. Their size is usually muchness than that of the fibres of Animal 

 life ; but, owing to the extreme variation in the flattening which they undergo, 

 it is difficult to make a precise estimate of their dimensions. Those of the 

 alimentary canal of Man are stated by Dr. Baly to measure from about ^ iVo 

 to ??T j-o part of an inch. They sometimes present markings, which indicate 



[Fig. 70. 



Another view of the stages of development of Muscular Fibre; 1, a muscular fibre of animal life enclosed 

 in its sheath or myolemma; 2, an ultimate fibril of the same; 3, a more highly magnified view of 1, 

 showing the true nature of the longitudinal striae, as well as the mode of formation of the transverse striae ; 

 the myolemma is here so thin as to permit the ultimate fibrils to be seen through it; 4, a muscular fibre of 

 Organic Life with two of its nuclei; taken from the urinary bladder, and magnified 600 diameters; 5, 

 muscular fibre of organic life from the stomach, magnified the same.] 



