438 
ON THE ACARUS. 
diately under the outer skin. On these passages, or, rather, near 
to them, were small bladders, which contained a clear fluid. The 
acari were neither to be found on the skin nor in the passages 
or bladders. 
From the fifth until the twelfth day the irritation gradually 
diminished, and at length entirely ceased. The bladders gra¬ 
dually dried up; the passages became less visible, and, on the 
twelfth day, the upper skin appeared covered with little dry 
scabs, which easily loosened themselves, and left behind a healthy 
skin. The results of these experiments prove that the horse 
acari will pass on to the human being, and thereby cause an itchy 
eruption on the skin; and also that, in many cases, the disease 
is not of long duration, and will get well of its own accord. 
I must mention, however, in opposition to the results of these 
experiments, that Greve states that, in many cases, the disease 
produced in the human being by the horse acari will last for three 
to six or even eight weeks. 
These observations are interesting, because they shew that the 
horse acari will live longer on a human skin favourably disposed 
for their existence than they will in glasses or any thing else 
without nourishment; but that they are incapable, in either way, 
of producing another generation. 
Greve considers it surprising that the horse itch is capable of 
being communicated from one man to another. I saw a case of 
this kind in the veterinary school in this town, where one of the 
grooms took the disease from a horse, and communicated it to his 
wife. There was another case, in which a person had it more 
severely, and for a longer time; but he did not infect any one, 
although manifold opportunities were offered. 
It is, I think, not at all wonderful that an insect so tenacious 
of life, and which can so easily adhere to any body as the acarus, 
should be communicated from one person to another. 
I have not, as yet, been able to succeed in discovering whether 
the horse acari have the power of producing mange in cattle, 
sheep, goats, dogs, and cats. 
The mange of cattle contains a species of acari which were 
first discovered by Gohier, at Lyons, in the year 1814, on some 
Hungarian oxen, which were driven after the Austrian army for 
the subsistence of the troops. They were so thin, and so eaten up 
by mange, that if a small quantity of dust was taken from 
their backs and examined, it was found to contain a great num¬ 
ber of the acari. 
When examined under a microscope, there appeared to be no 
perceptible difference between these insects and the horse acari; 
but no proofs have been given that the acari taken from these 
