_Moschus ex vesicis_ is said to be the musk taken from Tonkin sacs. As a rule, however, it consists of a mixture of musk substance taken from good sacs which present a bad appearance, or have been torn, and from sacs of an inferior quality, frequently adulterated with foreign substances, such as dried blood, dung of birds, weathered bicarbonate of soda, etc. To open a musk sac, cut it with a sharp penknife around where the hairless side joints the hairy side, and empty it by scraping it out upon a sheet of paper. The membranes and hair are then removed by means of pincers. The musk-substance of the Tonkin sacs is generally a heavy, dry-feeling mass; it is partially intermingled with and partially enveloped by small, thin, soft, brown, somewhat transparent membranes and frequently mixed with small hair. It is partially loose and crummy, and partially consists of various lumps or grains of the size of a mustard seed to that of a pea, which are more or less roundish, more seldom angular, softer or harder (but can always be readily cut), of a fatty lustre and black-brown or dark-red color. In fresh sacs, the mass is frequently soft, and, when bruised, somewhat smeary, but never unctuous. On rubbing, it becomes paler in color, and glistening hair-like, paler, gray or whitishyellow particles, sometimes of a crystalline texture, appear. The odor of the musk substance is peculiar, strong, and very constant; it is agreeable only when much diluted. Musk is not a substance of a constant chemical and physical constitution, the reason for this being found in the age and the different foods of the musk animal, the season in which it is killed, and the degree of dryness of the musk-substance. Water dissolves ¾ of good musk and 90 per cent. alcohol ½. The alcoholic solution is not precipitated by water. Musk further contains fat-like substances, wax, gall-substances (together 10 to 12 per cent.), glue-substances and albumen (6 to 9 per cent.), traces of lactic and butyric acids, phosphates, sulphates and hydrochlorates of the alkalies and alkaline earths, frequently strong traces of ammonium carbonate and a volatile oil, further moisture, humus-substance, and fibrous matter. Musk, when dried, has a weak odor, which gradually becomes stronger on moistening. There are several substances which destroy the musk odor, especially bitter almonds, camphor, sulphur, acids and sulphates. The odor adhering to a mortar in which musk has been rubbed can best be removed by pounding bitter almonds in it.