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100 | THE Microscopn. 
found the acari in seventy-two out of the hundred, or 72 per cent. 
This, however, is probably a rather large percentage, and does not 
represent quite an average of’ healthy persons, as most all of them 
were under treatment for cosmetic troubles. While connected with 
the Philadelphia Hospital for Skin Diseases, some years ago, I exam- 
ined comedones from one hundred and fifty persons, with the result 
of finding the acari present in 76 per cent. But the entire one 
hundred and fifty were suffering either from acne, commonly known 
as “ pimples,’ or comedones, popularly called “‘ blackheads,” or some 
other disease due to a local ill function of the skin. Now while 
Acarus folliculorum, unlike his fellow acarus, Sarcoptis scabiei, does 
not appear to have any causative relation to any form of disease of 
the skin, yet it is only present when the dilatation of the duct wall 
is marked. They tend rather to decrease than to cause the trouble, 
by eating up and disintegrating the plug of hardened secretion. 
As regards the location of the infested follicle, the greatest 
number, as well as the largest, longest, and healthiest looking speci- 
mens of Acari folliculorum, are to be found in the follicles of the 
skin in the region of the alz nasi; while the shorter, smaller, more 
dried-up looking individuals infest the skin of the nasal and super- 
ciliary ridges of the human face, and some few are present in the 
follicles of other portions of the body. The reason for this varia- 
tion in the size and distribution of the Demodex folliculorum is the 
relative variation in the lumen of the duct, and the diversity of den- 
sity and nutritive quality of the plug occupying the ducts of the 
respective glands. 
The Acarus folliculorum is also found between the hair-cylin- 
der and internal root-sheath of the hair-follicles, from which cireum- 
stance it has been called the “‘hair-sac mite.” These acari are also 
found in animals other than man: the dog, wolf, and horse being 
infested. I myself have found it in the cow, in whom it is relatively 
more tapering and slender, though larger, than in man. 
With regard to the preparation of this mite for the microscope, 
the mode of procedure is to squeeze the plug of secretion from its 
position in the face. Then teaze out the mass in glycerine, cover 
with a cover-glass and place under pressure till all the air is 
expelled, when it is ready for examination. When found, if still 
clinging to a portion of sebaceous matter, the cover-glass may be 
gently moved to and fro with a handled needle, while keeping the 
animal in view under a low power, until it is floating free in the 
glycerine, when it can be examined, turned over and manipulated. 
Or it may be isolated from the debris, and permanently mounted. 
