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Chemical Constitution of Voluntary Muscle

substance, fibre, death and band

CHEMICAL CONSTITUTION OF VOLUNTARY MUSCLE.

plained by supposing that a muscular fibre is made up of two kinds of substances, one doubly refractive, the truly contractile substance, which exists in the form of minute columns or pillars (sarcous elem en ts)set in rows across the breadth of the fibre, embedded among the second singly refractive and non-contractile substance. A very slight amount of the embedding material is present between the columns of a row, so that they present the appearance of a continu ous dark band. But there is a considerable accumulation of the embedding substance at the ends of the columns of one row, separating them by a clear-looking interval from those of the next row. Thus the dark band alternates with a light band, and the appearance of a cross striation is produced. Delicate mem branes, connected with the sarcolemnia, cross the fibre like partitions, dividing it into coin partments, and these partitions pass across in the region of the accumulation of embedding material, appearing as dark lines in the light band. It is only by special means that these details of a muscular fibre can be revealed. Fibres are collected into bundles and inclosed in a connective tissue sheath to form what is called a fasciculus ; and a number of the fasci culi are bound together by a denser layer of connective tissue to form a muscle.

Within its sheath a fibre in the living state is semifluid. The semifluid substance can be

squeezed out, and is called muscle plasma. When allowed to stand the plasma coagulates, and then separates into a watery portion called serum and a solid portion or clot, which con sists of a substance related to white of egg. The serum consists largely of water, but con tains also a substance like white of egg, al buminous, that is to say, as well as animal starch, and salts, chiefly of potash, and waste substances formed by the action of the muscle. The clear semifluid substance of the fibres in the living state becomes after death opaque and coagulated. It is the occurrence of coag ulation that produces stiffening of the body, or rigor mortis (the stiffness of death) as it is called, which conies on some time after the death of a person or an animal. The stiffening may come on quickly, within an hour or two after death or even sooner, if the person has died of an exhausting disease, and then it passes off quickly. The stiffening may be long delayed, as in the case of persons who have died in full vigour, by a sudden accident, for instance, and when it does at length occur it lasts long, and may continue even for several days. In both cases, after rigor mortis has dis appeared, the muscles become soft and flabby, and decomposition ensues.