346 ON THE CONTAGION OF ITCH OR MANGE. 
1st, That the serosity contained in the vesicles, or the pus 
in the pustules, was not found to include the active principle of 
contagion. 
2d, That ten living acarus, reduced to magma and inocu- 
lated upon the arm, determined the eruption of a pustule at the 
seat of inoculation, and of papulae in the vicinity. 
3d, That a living acarus deposited upon the skin is capable 
alone of producing signs amounting to the pathognomonic cha- 
racters of itch. 
Two years of daily contact with itched persons having failed 
in producing the malady, I was obliged to take some acarus and 
suffer them to penetrate my epidermis, that I might exactly ap- 
preciate the whole of the phenomena accompanying the con- 
tagion of itch and its development. 
A work on the contagion of itch, as it affects animals down- 
wards, requires an examination into the various authors that 
have treated on the subject, and the submission of any fact that 
might be doubtful to past experimentation. 
This memoir is divided into two parts ; one treating of the 
subject of contagion, the other of the treatment of itch. 
On the Contagion of Itch (or Mange) from Animals to Man. 
The transfer of itch from animals to man is now-a-days ad- 
mitted by all the world, as well by people whose judgment is 
instinctive as by medical men who base their opinions on ob- 
servation. Nothing is more common than to see itchy patients 
presenting themselves at the Hospital of Saint Louis, with tales 
of having contracted their malady from some horses they have 
been looking after, or from some cat or dog with which they 
have had constant intercourse ; and up to this very day, the 
professional man, so far from calling in question the assertion 
of the patient, has confirmed it. So that, in fact, the contagion 
of the itch from animals to man seems to be established by a 
multitude of observations. 
We are going succinctly to analyse these facts of contagion : 
though, first of all, we would state by what criterion we shall 
examine them ; since, should the data of the problem be clearly 
established, its solution will follow as a logical deduction. 
We shall divide the facts intended to be brought under discus- 
sion into two categories. The first will include those having re- 
lation to mangy animals upon which the acarus has never posi- 
tively been observed ; the second, such facts of contagion as 
regard animals really infested with the acarus, and suffering 
from mange. By this means we shall reduce to nothing those 
observations in which there exists any question about the pre- 
sence of an insect, and we shall also set a proper value on cases 
where contagion was barely possible, admitting that the ele- 
