ON THE CONTAGION OF ITCH OR MANGE. 347 
ments of contagion existed. So that, as to Bose* * * § , Gohiert, 
HertvvigJ, Bounes$, and HeringJ having met with insects on 
dogs pretended to be mangy, there is no proof that such insects 
were sarcoptes. In a disease which admits of the fact being 
scientifically demonstrated, it is not sufficient to say, as Bose 
has done — “ T have observed some insects on a mangy dog;” 
or, as Gohier, “ I examined through a magnifying glass the 
acarus of the dog in April 1813; it did not seem to me to pre- 
sent any remarkable difference from the acarus of the horse;” 
or, like Hertwig, “ The acarus of the dog has its body more 
thickly covered with hair than that of the horse;” or, as Bounes, 
“ That the sarcopte of the dog presents differences sufficiently 
distinctive from that of the horse ;” or, lastly, as Hering, “ That 
he has found the acarus of the dog in an ulcer upon the concha 
of the ear; the same acarus that he has since seen upon the 
ulcered foot of a horse.” For our own part, we cannot in these 
assertions discover irrefutable proof of the presence of an insect 
peculiar to the mange of dogs; and since, as a principle, every 
thing tends to the belief that there is such a thing as the 
sarcopte of the dog, we cannot outstep observation, and out of 
a supposition run on to the reality. We have also found, as 
we shall by-and-by point out, a microscopic insect upon dogs 
affected with skin disease, but we have not from that fact con- 
cluded that the insect was the acarus of mange. But although 
we place in doubt the existence of the sarcopte that would cause 
mange in dogs, and, a fortiori , the possibility of the spreading 
of the disease to man, we are not to be regarded as considering 
of no value cases of disease of the skin contracted by man 
through contact with the dog suffering under cutaneous disease. 
If we deny contagion in-so-far as the mange is transmitted by 
an insect, we cannot deny the influence of contact with an 
animal having disease of the skin as a cause of cutaneous dis- 
ease in man. In a word, there are two kinds of facts here, 
one requiring scientific demonstration, which we reject; the 
other requiring no more than constant relation between cause 
and effect to be kept in view, which we accept. Among these 
last may be mentioned the veterinary pupil, of whom GrognierIT 
speaks, who had hands and arms covered with itch, after hav- 
ing well rubbed a mangy dog; the child who took the itch 
* Cited by Hering, in his memoir. 
f M^moires et Observations de Chirurgie et de Medecine V6t6rinaires. 
\ Cited by Hering. 
§ Compte-Rendu de l’Academie des Sciences, 1838. J. H. Half-year. 
|| Die Krotzmilben des Thiere und cinige verwandte Arten. Nach eigenen 
Hutersuchringen beschrieben. In nova acta Phisico-Medica, vol. xviii, & 
Pari. 
5f Compte-Rendu des Travaux de PEcole V6t6rinaire de Lyon pour 1817. 
