70 
Parasites of Cattle and Sheep. 
substance, forming a minute channel. As she proceeds, she 
deposits her eggs, and when the process is completed, dies. 
The eggs, as embryos, pass singly out of this little channel and 
become fecundated by the male on the surface of the skin, and 
the females of this generation repeat the process of boring 
and hatching a new generation ; so that the skin of the animal, 
the subject of sarcoptic mange, has on its surface mature and 
immature parasites commencing to bore, or developing for this 
purpose, while in the substance of the skin are eggs and embryos. 
It therefore follows that while dressings applied to the skin 
may kill the parasites on the surface, the coming generation, 
protected by its position in the little channel, must be provided 
against by repetition of the dressing. The form of disease 
caused by this parasite is usually found on the upper surface 
of the body, and tends to spread at the border of the lesion. 
The irritation is greater than in the other forms. 
The other two varieties, psoroptic and symbiotic, which 
may be found together on the same animal, usually attack the 
root of the tail and the neck, and the Psoroptes have a greater 
tendency to spread to other parts of the skin, while the 
Symbiotes, which live together in groups, rarely wander from 
their common seat, the root of the tail. Neither of these acari 
burrows. 
Symptoms . — These result from irritation caused by the 
pricking of the parasites, and possibly the insertion of some 
irritating substance. The degree of irritation varies ; in some 
cases it is slight, in others it is intense, and the animal may 
be much disturbed, rubbing violently, and sometimes severely 
injuring the skin, which, in the sarcoptic variety, may become 
thickened, hard, and wrinkled. Cattle out of doors appear 
less affected ; indeed, it is asserted that turning out to grass 
is a cure. This is doubtful, for it is often found that on 
returning to the house the disease again becomes active ; and 
though the possibility cannot be denied, spontaneous cure 
is not common. 
The diagnosis absolutely depends on discovery of the 
parasite, which is accomplished by aid of the microscope. 
Treatment . — Though there is little disposition for the 
acarus to leave its host, and it cannot live and develop apart 
from him, it is liable to removal by various means, as by 
animals rubbing each other, &c., and the disease must be 
regarded as contagious and treated accordingly. Affected 
animals should be isolated. If the disease is recent and 
limited, it may suffice to dress the affected parts only ; but if 
there is any doubt on this point, and usually there must be, 
it is advisable to apply the dressing all over the animal. • The 
skin is better prepared for receiving the dressing if washed 
