OR INSECT OF ITCH AND MANGE. 
371 
pressed on each side, and formed sometliing like a turtle; white, 
variegated by stripes, and the back roughened by hard warts. 
Of the eight feet, the four front ones are situated near the head, 
and in the form of a hand; the four hinder ones are farther from 
each other. The four front feet are also furnished with a species 
of sucker. 
Species I. Sarcoptes hominis. —Insects found on human beings 
who have the itch : acari scabiei. 
Species II. Sarcoptes Equi. — Insects found in the pustules of 
mange in the horse. 
Raspail mentions no other species; but he says, that, no 
doubt, it will one day be discovered that the pustules in every 
kind of animal having the itch contain a different species of 
insect. It was not known to him that Walz had already, in the 
year 1812, found acari in scabby sheep and foxes; and had 
depicted those of the sheep ; and also that Gohier had, in the 
years 1812 and 1814, found acari on horses, children, dogs, cats, 
and rabbits affected with mange, and had given drawings of 
those taken from the horse, in his Memoires et Observatio)is sur 
la Chirurgie et la Medecine Veterinaires, tom. ii, 1816; and 
that Bose (in his Diction, des Scien. Medicales, tom, xvii) had 
also given delineations of the acari scabiei of the horse, the 
sheep, and the cat. 
The natural history of this insect in the human being is, up to 
the present time, very imperfectly known. It is probably to be 
met with in all countries and in all climates. It is known in 
Greenland {Fabricii Fauna Groenlandicaj 1780, p. 73); but it 
is oftener found in the southern countries than in the northern ; 
at least, they have been frequently observed in Spain and Italy. 
They are also found to appear in greater numbers in particular 
seasons or years. It is not yet decided, although very probable, 
that similar observations may be applied to the development of 
many other insects. This insect, living only on and beneath the 
skin of men, is in no case known to pass to any other animal. 
It, however, lives a considerable time when removed from the 
skin. How long this is possible, under diflerent circumstances, 
is not yet clearly ascertained. According to some experiments 
made by Albin Gras, it appears that they can live in pure water 
three hours; in vinegar, in alcohol of thirty degrees, and in a 
solution of kali carbonicum, twenty minutes; in a solution of 
sulphuric acid and kali twelve minutes; in turpentine nine 
minutes; and in a solution of arsenic four minutes. When not 
exposed to such violent and destructive measures, it has been 
said that the insect will retain life for five or six days; but, 1 
believe, from a comparison of the acari of mangy animals. 
