ACARIIS FOLLICULTRIIN is the most generally accepted name for a microscopic parasite residing in the sebaceous sacs and hair follicles of the human skin. It is also known as the demodex folliculorum, the generic name being derived from the Greek words demos, lard, and (fix, a boring worm. It was first described by Dr. Simon of Berlin in 1842, under the title of aearus folliculorum, which was suggested by the eminent zoologist, Erichsen of Berlin. In the following year, 111r. Erasmus Wilson made it the subject of i an elaborate memoir, which appeared in the Philosophical Transactions, in which, as there are doubts as to its exact zoological position, he simply terms it the entozoon folliculorum. According to professor Owen, who gave it the name of demodcx, it represents the lowest form of the class arachnicla, and makes a transition from the annelids to the higher articulata. As regards the size and form of these animals, there is much variety; they pass their whole existence in the fatty matter of the sebaceous cells, moult ing repeatedly during their growth, and being finally expelled from the fol. ,,S licles with the secretions of these organs. Their presence has no . p o M once, according to r. Wilson, to disease of the skin or of the follicles. cc ith They are met with in almost every person, but arc most numerous in c .--' c those in whom the skin is torpid, in invalids, and in the sick. They vary c e in length from Atli to of an inch, and the accompanying figure c -..', z.s. , represents the magnified parasite. Their number is various; in some per- sons not more than two or three can be found in a follicle, while in others ::!-; Mr. Wilson has seen upwards of fifteen. The head is always directed in-,--4:-.
wards, and when a number are present they seem to be collected into a if :..:L conical bundle, the larger end of the cone being formed by their heads.
The situation in which they are most commonly found is the skin of the -4-..?, -.1 face, and particularly that of the nose, but they have also been met with in the follicles of the back, the breast, and the abdomen. As far as we know, they are never found on the limbs. ,...i .., A reference to the figure shows that the animal possesses eight thoracic appendages (e, e) of the simplest and most rudimentary kii.d, each of which is terminated by three short sate. The integument of the abdomen is very finely annulated. The mouth is suctorial or probosidiform, consisting of ) two small spine-shaped maxillae (b), and an extensive labium capable of being elongated or retracted; it is provided on each side with a short, thick, maxillary pulp (a. a), consisting of two joints with a narrow, triangular magnified. labrum above. The sexes are distinct, but the differences between the male and female are not well recognized. Ova are frequently seen, both in the body of the female and in detached discharged masses. Any of our readers may readily observe their own acari 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. Very similar if not identical animals have been found in the contents of the pustules of mangy dogs.