280 DADD’S VETERINARY MEDICINE AND SURGERY. 
pest—-one which appears to form an integral part of that curse 
inflicted on the whole creation by the fall of man. 
The importance of cleanliness, and its concomitant health, to 
prevent contagion, may be further illustrated. We have just seen 
above that an acarus, although a loathsome pest, is yet very nice 
in its taste, and particular about a nidus in which to deposit and 
hatch its eggs. It enjoys the highest degree of prosperity on the 
unhealthy skin, multiplying there fastest; su that if it creepe 
from it to the opposite—the sleek, healthy one of the horse or ox, 
or dry wool of the sheep—it feels itself from home, and, before it 
even reaches the skin, may be bruised or shaken off. If, however, 
it creeps upon the unhealthy animal with its staring coat, it soon 
reaches the skin, aud commences its direful work, every thing 
there being congenial to his happiness; hence the incredible 
speed at which it propagates its species, until it either consumes 
its victim alive, or is arrested at its fatal work by the timely 
unguent of the veterinary surgeon. 
Again: wheu a dirty animal shakes itself, as it invariavly does 
after rubbing itself against any thing, less or more scurf, dan- 
druff, and dust is thrown into the atmosphere, and carried to a 
distance by high wind. Now, under such circumscances, whea 
affected with scabies, it is manifest that the smallest of these pung 
insects, as well as their eggs, will be blown frors one pasture to 
another; that the latter will lodge in the dirty staring coat of 
the unhealthy animal, when they will be blown off that of the 
clean sleek one, or be brushed off before they reach the skin, or 
any nidus capable of hatching them. In this manner we can 
trace contagion from one animal to another, and thus account, in 
harmony with entomological science, for what has hitherto been 
termed spontaneous cases of scabies in some of our domesticated 
animals, while others have escaped the disease, though all herd- 
ing together in one field. We can also account for the fact why 
the disease is more liable to break out among sheep than horses 
and cattle, without coming in contact with strange flocks, because 
the coats of the latter are more likely to be impregnated with 
eggs than those of the former, while they afford a better nidus for 
hatching them. 
With vegard to health, it has even been said that the blond of 
scabbed animals is diseased; nay, that the blood of all animals is 
loaded, more or less with the eggs of acari, and that they are 
