ON TRACHEAN ARACHNIDA. 
533 
of its spoil was covered, from the effect of the preparation it 
underwent to preserve it, with an innumerable quantity of 
mites, almost invisible, being scarcely the twentieth part 
of a line in their greatest diameter. Examined with 
the microscope, some of these mites, the smallest, appear to 
have great relations with the itch-mite, and others, with that 
which infects sparrows, Acarus passer inns, Lin. 
The persons who prepared the animal, had their arms very 
speedily covered with small irritating pustules, occasioned by 
the introduction of the mite into the skin. 
The study of these little animals is of the greatest interest, 
not only to the naturalist, but also to the physician. It appears 
by the best observations that the ulcers of the itch, both in 
man, horse, dog, and cat, almost always exhibit mites ; and 
that these animals, impregnated with the morbific virus, can 
communicate it. But this circumstance excepted, it remains 
an undecided question, whether or no they are the primary 
causes of this malady. That they may establish themselves, 
and propagate in sores favourable to their development ; that 
they may aggravate the malady in proportion to their multi- 
plication ; and that they may spread over other parts of the 
body, we may very naturally and easily conceive ; but to draw 
any further conclusions, appears to be somewhat precipitate. 
Through an injudicious rage for generalization, the origin of 
the dysentery has been attributed to a species of the same 
genus ; and Olivier was even of opinion that a similar cause 
might have given rise to the plague. 
