Muscle, or Mussel, Mytilus, L. in ichthyology, a genus of shellfish, consisting of several species; the following of which are the principal; viz.

1. The margaritiferus, or pearl-bearing muscle, having a compressed shell, the inside of which is exquisitely polished, resembling in whiteness and brilliancy the real pearl. After being divested of its external laminae, by aquafortis, and the lapidaries' mill, the outer part acquires a similar lustre.- This is the true mother-of-pearl shell, which is converted into various toys, such as snuff-boxes, buttons, spoons, etc.

2. The edilis, or eatable muscle, which has a strong shell slightly curved on one side, and angu-lated on the other. It is found in immense beds, both in deep water, and above the low-watermark, in the British seas.

The muscle is not only persecuted by numerous enemies, in its own element, but also subject to certain diseases, which have been conjectured to be the cause of the ill effects consequent on the eating of these shell-fish. There are two disorders of that tendency, which, by Dr. MCEHRING, are termed the moss and the scab. The former is occasioned by the roots of moss being introduced into the shell, so that the water penetrates, and gradually dissolves the fish. The scab is caused by tubercles, that are produced by the dissolution of the shell.

Whatever may be the cause, it is well ascertained, that the eating of muscles has sometimes produced cutaneous eruptions ; restlessness and agitation ; an insupportable itching throughout the whole body, together with erysipelatous inflammations. These complaints, however, may be easily removed by the liberal use of oil, emetics, and of milk; as they have in no instance proved mortal.

The edible muscle, nevertheless, furnishes a rich food, though it be difficult of digestion. Even in a sound and fresh state, it is to some constitutions hurtful; and, if contaminated by disease, it becomes, in some degree, poisonous.- As muscles are most detrimental to health, when eaten raw, it will always be advisable to boil them with onions; but they should be previously washed with vinegar, and seasoned with pepper: thus qualified, they cannot be injurious, unless eaten to excess, or too frequently,