306 
ACARUS SCABIET. 
by whom they were tended and rubbed had not contracted the dis- 
ease in the present and many preceding instances; while a dog, 
from having slept on the straw which had littered one of the mangy 
animals, was seized shortly after.” The experiments of Gohier, 
who endeavoured to inoculate animals of one genus with the acari 
of another, tend likewise to strengthen this opinion. But it is time 
we turn our attention to the remaining part of the question, viz. 
Can a man affected with scabies impart the same to a brute 1 Some 
writers assure us that dogs have contracted this disease from their 
masters; but I have been unable to meet with a well authenticated 
instance of this upon record, nor has such a case fallen within the 
observation of that distinguished veterinary surgeon Mr. Youatt : 
yet, if we admit the possibility of acari from animals locating them- 
selves on the human subject, and producing thereby an itchy erup- 
tion, bearing so strong a resemblance to scabies that all authors 
have agreed in giving it this name, it is surely not impossible that 
the sarcoptes hominis may have been transferred to animals, and 
thus produced in them an analogous disease. But this is arguing 
for the parasitic origin of scabies; which if we deny, will oblige us 
to seek for some other cause to explain the transmission we are sup- 
posing to take place : in this case I grant the possibility is consider- 
ably diminished, for we must then presume the fluid of the mangy 
sores to be the contagious principle — a presumption highly impro- 
bable. If the serosity taken from the vesicles of scabies in the 
human subject is inadequate to produce that disease in an indivi- 
dual of the same species, a fortiori it must exert still less power in 
inoculating animals which are confessedly and notoriously exempt 
from the contagious influence of morbid human poisons. Except 
the saliva of a rabid man, I am not aware that any other morbid 
fluid of our species is capable of communicating a disease to the 
brute analogous to that by which it was secreted : two of the most 
active and baneful of these poisons, to wit, those of syphilis and 
variola, produce no effect when applied to the organs of genera- 
tion and skin of animals. With these facts before us, then, we 
are bound to reject this explanation of a not improbable hypo- 
thesis. What now is the resume of this and the two preceding 
letters, and what conclusions may we thence deduce ? 
1st. That parasitic insects, called acari, or sarcoptes, are met 
with in many cases of scabies, but in no other disease. 
2d. That our not being able to detect them in every case, does 
not warrant us in denying their presence at some period or other 
of the disease; nevertheless, till such presence be demonstrated, 
we are justified in withholding our assent to their being the sole 
cause of scabies. 
3d. That the acari are never found within the vesicle or pustule, 
