ON THE CONTAGION OF ITCH OR MANGE. 351 
dry itch. After much inquiry it came out that, eight days be- 
fore the disease made its appearance, a young cat having the 
itch had been seen lying upon the neck and arm of the child 
while asleep. 
Such are the facts of contagion mentioned by observers. 
None of them, it will be seen, have put themselves to the 
trouble of discovering the insect either upon the mangy animal 
or the person who caught the itch from it ; so that, in spite of 
our best inclinations, we are forced back to the point of deciding 
upon, not the contagion of itch of a disease caused by a sarcopte 
peculiar to the itched animal, but upon purely and simply the 
development of a disease of the skin, contracted through con- 
tact with an animal suffering itself from a cutaneous disease. 
Having thus far given the results of the observation of our 
predecessors, we shall now submit our own on the subject. 
All the patients admitted for having caught the itch from 
horses, during our sojourn at the Hospital Saint-Louis, were 
submitted to careful microscopic examination, and were all dis- 
covered to harbour the acarus of man or else to be simply 
affected with prurigo. But all these facts put together, those 
borrowed of authors as well as those furnished by ourselves, 
still require confirmation by direct experiment ; and this ex- 
perimentation we have put into practice, as regards the con- 
tagion of mange affecting horses and dogs. 
M. Delafond, professor at Alfort, sent me about fifty acarus 
taken from a mangy horse, which were kept alive for ten days 
amid detritus and epidermic scales and incrustations. On the 
3d June, one of these acarus was placed upon the back of the 
hand of a man by the name of Francis, in the service of M. Bazin. 
For half an hour I watched every movement of it through a 
microscope, in the expectation of seeing it enter some groove 
and conceal itself, as the acarus of man never fails to do. But 
this proved vain. I then detached the epidermis, and with care 
placed the insect underneath the epidermic follicles still left 
adhering : indeed, I traced out for it the entrance to a groove. 
The acarus made haste to creep into it at once, under our eye, 
filled itself with nutriment, and, having satisfied its hunger, 
began again to run about in all directions without once making 
a breach in the epidermis. At the end of an hour it was trans- 
ferred to the left fore-arm of the same subject, in company with 
two other acarus, underneath a watch-glass which I had firmly 
fixed to the part by bands very moderately tight, for a special 
reason. Some hours after, the apparatus became displaced, as 
I anticipated it would, and the three acarus had full liberty to 
wander upon the body, and so effect a transmission as direct as 
it was possible. This was immediately followed by pricking, 
