THE MICROSCOPE. 99 
greater or lesser extent, in almost every one. This condition of 
torpidity produces an abnormal consistency of the secretion, on 
account of which the products of the gland-cells accumulate in the 
duct as a hard plug, instead of escaping at the free extremity of the 
tube, or pore, as an oil for the proper lubrication of the skin. Dirt 
accumulates in the exposed extremity of the plug, and then we have 
a comedone, or as it is commonly called, a blackhead. Such is the 
habitat of this parasite. In this constantly warm and comfortable 
nidus the acari breed and proliferate, though not with startling 
rapidity. A rather remarkable fact is that both old and young acari 
constantly maintain the same relation to the follicle. That is, the 
axes of their bodies are always nearly parallel with the axis of the duct 
of the oil-gland, the tail almost invariably pointing outward, and the 
head directed inward toward the floor of the follicle, as if the animal 
~ had crawled into his position from without. To use a nautical term, 
they always lie “head on.” 
Sometimes ladies whom I am treating for cosmetic troubles, will 
ask me for some medication to remove the “worms” (!) from their 
faces, under the impression that the comedone, or blackhead, is alive! 
This impression is partly due to the appearance of the unctuous 
plug when squeezed out, and partially also to the advertisements of 
quacks, who make capital out of the proven presence of the innocent 
little Demodex, and blame him with causing the very trouble which 
he is doing his best to relieve. 
The number of acari present in a single follicle varies from one 
to twenty, there being much diversity of numbers according to the 
age and condition of health of the host, and also according to the 
location of the follicle. Though they are to be found in the skin of 
persohs of any age, sex or condition of health, yet local and general 
ill-health and the waning powers of old age, seem to be the condi- 
tions most suitable to the entertainment and proliferation of the 
parasite. Notwithstanding this, the Acarus folliculorum is to be 
found in persons entirely healthy in every respect, unless, indeed, 
‘dilatation of the follicles be considered a diseased state of the skin. 
But since everyone living in cities, at least, has this dilated condi- 
tion, the presence of the parasite may be considered the rule, and its 
absence the exception. Gruby found acari in forty out of sixty per- 
sons, or 663 per cent. Wilson found a larger percentage. Some 
naturalists, as Megnin, have only found the parasite present in ten 
per cent. I myself have, within the past two years, examined come- 
dones from one hundred persons, chiefly ladies, in this city, and 
