CASTOREUM, an oily viscid gland secretion contained in two pairs of membranous sacs between the anus and external genitals of both the male and the female Russian and American beaver ; known also as beaver musk. After drying, it comes into commerce as more or less solid masses, of brown colour and a strong, rather disagreeable odour, due to the presence of about 2% of an essential oil, in addition to which a number of odour Iess organic and inorganic substances have been isolated. It was formerly used medicinally as a stimulant in hysterical affections, but at present serves almost exclusively for blending perfumes, in the same way as musk and civet, usually in the form of an alcoholic extract.