AC'ARUS FOLLIC'ULO'RUM, or Dentodes-, oc Stcatanon follieulornm, the commedo mite. A microscopic parasite residing in the sebaceous sacs and hair follicles of the human skin. It was first described by Dr. Simon of Berlin in 18-42, under the title of Acarus folliculorum, which was suggested by the eminent zoologist, Eriehson of Berlin. Ac cording to Professor Owen, who gave it the name of Demodex, it represents the lowest form of the class Ar achnida, and makes a transition from the An nelids to the higher Ar ticulata. Their pres ence has no reference to disease of the skin or of the follicles. They are met with in almost every person. They vary in length from to of an inch, and the accompanying figure represents the magnified parasite. Their number is various; in some persons not more than two or three can be found in a follicle, while in others upward of fifteen. The head is always directed inward. They are most com monly found in the skin of the face, particularly that of the nose; but they have also been met with in the follicles of the back, the breast, and the abdomen. The animal possesses eight thor acic appendages (c. c) of the most rudimentary
kind, each of which is terminated by three short The integument of the abdomen is very finely annulated. The mouth is snetorial or proboscidiform, consisting of two small spine shaped (b), and all extensive labium capable of being elongated or retracted: it is provided on each side with a short, thick. maxil lary palp (a, a). consisting of two joints with a narrow, triangular lahrum above. The sexes are distinct, but the differences between the male and female are not well recognized. Ova are fre quently seen, both in the body of the female and in detached discharged masses. Acari inay be examined by collecting between two pieces of thin glass the expressed fatty matter from a nasal follicle and moistening it with a drop of olive oil before placing under a microscope lens of 300 diameters. Identical animals have been found in the skin of dogs, hogs:and cattle. They damage in some instances. No treat ment is requisite.