502 OF NUTRITION. 



to be readily separable from them. It differs not, however, in any important 

 particular, from the same tissue elsewhere ; and the white and yellow fibrous 

 elements may be detected in it in varying proportions, in different parts, the 

 latter being especially abundant in the Skin and the Lungs, which owe to it 

 their peculiar elasticity. Hence the Mucous Membranes for the most part 

 yield Gelatin, on being boiled. There is some reason to believe, that the Skin 

 also contains non-striated muscular fibres scattered through it. The regene- 

 ration of all the forms of Mucous Membrane, after loss of substance by disease 

 or injury, is very complete, and takes place with considerable rapidity. 



642. The structure of the Muscular tissue has been already described in 

 detail (Chap, v.) ; and it only remains here to add, in regard to its origin and 

 development, that there seems reason to believe that the primitive fibres are 

 at first formed by the junction of cells of a cylindrical shape ; the cavities of 

 which coalesce, so as to become a continuous tube, the Sarcolemma ; whilst 

 from their contents, the fibrillse are ultimately generated. Their nuclei may 

 be brought into view in the fully-formed fibre ( 374) ; but are seen with least 

 difficulty in the non-striated fibres, which seem like striated fibres whose 

 development has been arrested. If the view which has been given ( 77) 

 respecting the continual death and decay of the Muscular tissue, consequent 

 upon the demand for its vital activity, should be correct, its growth must be 

 rapid, even in the adult ; and, as the difference in the diameter of the fibres 

 at various ages is very small, there must be a continual production of new 

 tissue, and not a mere expansion of the old. Notwithstanding this, it is doubtful 

 whether Muscular tissue is ever regenerated. Wounds of muscles are united 

 by Areolar tissue, which gradually become condensed, but its fibres do not 

 possess any degree of contractility. 



The solid matter of Muscle consists of little else than Fibrin; as will be seen from the 

 following analysis by Berzelius. It should be added, however, that it is impossible to 

 separate completely the vessels, nerves, areolar tissue and blood, from the muscular fibre 

 itself; and that the analysis cannot, therefore, be regarded as perfectly accurate in regard 

 lo the composition of the essential constituent. 



Fibrin 15-80 



Areolar substance --.... 1-90 



Albumen and Heematosine .... 2-20 



Alcoholic extract and lactates - - - - 1-80 



Osmazome (?) and watery extractive - - 1-05 



Phosphate of lime with albumen - - - -08 



Water and loss 77-17 



100.00 



Thus something less than 23 per cent, of solid matter exists in ordinary meat; and in 

 100 parts of this solid matter there are about 7 parts of fixed salts. 



643. The structure of the Nervous System, also, has been sufficiently dwelt 

 on in the former part of Volume ( 110 112). The production of its tubes 

 and their contents from cells, appears to take place on the same plan as that 

 of the tubular fibres of Muscle. From the large amount of Blood with which 

 the Nervous System is supplied, and from the tendency of its substance to 

 undergo rapid decomposition, it may be inferred that the Nutritive operations 

 are performed in this tissue with great activity ; and this appears to be espe- 

 cially the case at the central and peripheral terminations, where the Blood- 

 Vessels are most intimately connected with it. Reason has been given ( 77) 

 for the belief, that this tissue, like the muscular, is continually undergoing 

 waste and renewal ; with a rapidity proportional to the demand for its func- 

 tional activity. This change may be inferred to take place rather in the gray 

 substance than in the white; the functions of the former being an active 

 generating character, whilst those of the latter are more passive. Appearances 



