es,
however, according to the species of acarus which infests the skin, so
that we must treat of several different kinds of acariasis.

PARASITE: _Sarcoptes scabiei equi._ MALADY: _Sarcoptic acariasis._--This
is the special _Sarcoptes_ of the horse, but under favorable conditions
it can be transmitted to ass and mule, and even to man, and may live
indefinitely on the human skin. The mite (Pl. XXXIX, fig. 1) is nearly
microscopical, but may be detected with a magnifying lens among moving
scurf taken from the infected skin. Like all _Sarcoptes_, it burrows
little galleries in and beneath the scurf skin, where it hides and lays
its eggs and where its young are hatched. It is therefore often
difficult to find the parasite on the surface, unless the skin has been
heated by a temporary exposure to the sun or in a warm room. The mite
may be detected more readily by placing scrapings on black cardboard
and warming, or better by macerating scabs or scrapings in a solution of
caustic soda or potash and then examining them microscopically. Like
other acari, this is wonderfully prolific, a new generation of fifteen
individuals being possible every fifteen days, so that in three months
the offspring of a single pair may produce generations aggregating
1,500,000 young. The _Sarcoptes_ have less vitality than the
nonburrowing acari, as they die in an hour when kept apart from the skin
in dry air at a heat of 145 deg. F. They live 12 to 14 days apart from the
skin in the damp air of a stable. On a piece of damp hide they lived
till the twenty-fourth day, when they began to die, and all were dead on
the twenty-eighth.

_Symptoms._--The symptoms are an incessant, intolerable, and increasing
itching of some part of the skin (head, mane, tail, back, etc.), the
horse inclining himself toward the hand that scratches him, and moving
his lips as if himself scratching. The hairs may be broken and rubbed
off, but the part is never entirely bald, as in ringworm, and there may
be papules or any kind of eruption or open sores from the energy of the
scratching. Scabs of any thickness may form, but the special features
are the intense itching and the presence of the acarus.

_Treatment_ consists in the removal of the scabs by soapsuds, and, if
necessary, a brush and the thorough application of tobacco 1-1/2 ounces
and water 2 pints, prepared by boiling. This may be applied more than
once, and should always be repeated after 15 days, to destroy the