346 The American Naturalist. [ April, 
AN EXTREME CASE OF PARASITISM: 
By Ropert Hessier, A. B., M. D. 
There is a small family of minute animals belonging to one 
of the sub-divisions of the arthropods which is of especial inter- 
est on account of the parasitic habits of many of its members. 
One of these, Sarcoptes scabiei De G., is parasitic on the genus 
Homo. 
Historicat.—It seems that the Jewish physicians dwelling 
among the Moors of Spain, in the 12th century, knew some- 
thing about these animals and their causative relation to the 
affliction known as the itch. The discovery of the microscope 
early in the 17th century (1619) led to many investigations, 
some of which had reference to the itch mites. The first good 
description of the mite bears the date of 1687, and was written 
‘by Bonomo to Redi, at Florence. After this, various observers 
saw the insect, but frequently it was confounded with other 
mites, especially the cheese mite. Linneus in his Systema 
Nature, 1734, had a very imperfect idea of it.’ 
In the century following the first appearance of the Systema 
Nature, the mites, as causes of the itch, were frequently the 
‘subject of heated discussions among medical men. The iden- 
tity of the human itch mite was better known to naturalists 
than to physicians.’ For instance, in a large treatise on skin 
diseases by P. Rayer, originally published in Paris in 1835, 
the author, in describing the causes of the itch, says: “ Causes 
—Scabies is one of the most universally disseminated conta- 
gious diseases known; the most momentary contact of the 
fluid secreted by its vesicles is enough to communicate the 
infection ; it is observed in every climate during every season 
of the year, attacking all ages and persons in every rank of 
life, without discrimination. It is most commonly observed, 
however, among the poor and wretched,” etc. Further on he 
1 Read before the Indiana Academy of Science, December 28, 1892. 
2 Hebra, “ Diseases of the Skin,” 1868. P. 168-180 
3 Hebra, “ Diseases of the Skin,” 1868. P. 180-181. 
