ON TR ACHE AN ARACHNID A. 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 passerinus, 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 morbij&c 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 aggi'avate 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. 



