MUSCLE, in anatomy, a part of the human body, destined to move some other part, and that in general by a vo luntary motion, or such as is dictated by the will ; being composed principally of flesh and tendinous fibres, which have also vessels of all kinds, as arteries, veins, nerves, and lymphatics ; all which are surrounded by, or enclosed in, one com mon membrane. See ANATOMY.
In a chemical view, the muscular parts of animals are known in common lan guage by the name of flesh. They con stitute a considerable proportion of the food of man. Muscular flesh is compos ed of agreat number of fibres and threads, of a reddish or whitish colour ; these, after they have been acted on by water, in order to separate the extraneous matter from them, are left in the state of grey fibres, insoluble in water, and be coming brittle when dry. The substance possesses all the properties of Foil's', which see. Besides fibrin, they are found to contain albumen,gelatine, extractive, phosphate of soda, of ammonia, and lime.
The muscles of different animals differ exceedingly from each other in their ap pearance and properties, at least as arti cles of food; but we know little of their chemical differences. The observations of Thouvenel alone were directed to that object, and they are imperfect. The flesh of the ox contains, according to him, the greatest quantity of insoluble matter, and leaves the greatest residuum when dried; the flesh of the calf is more aqueous and mucous ; the land and water turtle yields more matter to water than the muscle of the ox ; but Thouvenel ascribes the dif ference to foreign bodies, as ligaments, &c. mixed with the muscle of the turtle. Snails yield to water a quantity of matter intermediate between that given by beef and veal : with them the muscles of frogs, crayfish, and vipers, agree nearly in this respect ; but the muscles of fresh water fish, notwithstanding their softness, yield a considerably smaller proportion. When meat is boiled, it is obvious that the gela tine, the extractive, and a portion of the salts, will be separated, while the coagu lated albumen and fibrin will remain in a solid state. Hence the flavour and the nourishing nature of soups derived from the extractive and gelatine. When meat is roasted, on the other hand, all these substances continue in it, and the taste and odour of the extractive is greatly heightened by the action of the fire. Hence the superior flavour of roasted meat. Fourcroy supposes, that the brown
crust which forms on -roasted meat is composed entirely of the extractive. The cuffs is a thick dense membrane, com posed of fibres interwoven like the tex. ture of a hat. When it is macerated for some hours in water, and agitation and pressure are employed to accelerate the effect, the blood, and all the extraneous matter with which it was loaded, are se parated from it, but its texture remains unaltered. On evaporating the water em ployed, a small quantity of gelatine may be obtained. No subsequent maceration in cold water has any further effect. When distilled, it yields the same pro ducts as fibrin. The concentrated alka lies dissolve it, converting it into oil and ammonia. Weak acids soften it, render it transparent, and at last dissolve it. Ni tric acid converts it into oxalic acid and fat, while, at the same time, azotic gas and prussic acid are emitted. When heated it contracts, and then swells, ex hales a fetid odour, and leaves a dense charcoal difficult to incinerate. By spon taneous decomposition in water or moist earth, it is converted into a fatty matter, and into ammonia, which compose a kind of soap. When allowed to remain long in water, it softens and petrifies, being converted into a sort of jelly. When long boiled in water it becomes gelati nous, and dissolves completely, constitut ing a viscid liquor, which, by proper eva poration, is converted into glue. Hence the cutis of animals is commonly em ployed in the manufacture of glue. From these facts the cutis appears to be a peculiar modification of gelatine, ena bled to resist the action of water, partly by the compactness of its texture, and partly by the vicidity of the gelatine of which it is formed; for those skins which dissolve most readily in boiling water af ford the worst glue. The skin of the eel is very flexible, and affords very readily a at proportion of gelatine. The skin shark also readily yields abundance of gelatine ; and the same remark applies to the skins of the hare, rabbit, calf, and ox ; the difficulty of obtaining the glue, and its goodness, always increasing with the toughness of the hide. The hide of the rhinoceros, which is exceedingly strong and tough, far surpasses the rest in the difficulty of solution and in the goodness of its glue. When skins are boiled, they gradually swell, and assume the appearance of horn ; they then dis solve slowly.