Small-Pox in Sheep. 
555 
from what wo see of the progress of the affection in a large lot of 
sheep, and from the experiments made with a view to determine this 
important point, we have come to the eonclusion that there is little 
variation in the time of incubation. The disease may appear on 
the ninth day, or may be protracted to the eleventh ; but speaking 
generally, ten days may be regarded as the period of incubation. At 
the end of this time the sheep sickens, refuses its food, has a hurried 
breathing, accompanied by a hot state of the skin, an almost un- 
quenchable thirst, a bloodshot condition of the eyes, and a discharge 
from the nostrils. All these arc indications of the febrile state of the 
system, and simultaneously with it a particular eruption takes place 
on the body. If the eruption is very copious, the case assumes 
what is generally called the confluent form ; that is to say, the papula; 
(or pimples) coalesce and run together, as it were, in chains. At 
times tho papula? arc distinct and separate, and then we speak 
of the case as mild. We divide the small-pox in sheep, therefore, 
into two varieties, the same as in the human subject, — the benign 
small-pox and the confluent small-pox. This, the second, stage of 
the disease, speaking of the condition of the skin alone, lasts for three 
days, when a peculiar change is observable in the papula?, which, 
instead of being red, and thus showing a high degree of inflammation, 
assume a white appearance. Invariably, when the disease has reached 
this point, there is a slight abatement in the severity of the symptoms. 
The fact is very remarkable, that the morbific matter which has 
entered into the organism of the animal, through the medium of the 
tainted air, and has been lying hidden for ten days, has nevertheless 
during the whole of that time been appropriating to itself some of 
the materials or constituents of the blood, and nmltiplying to such 
an extraordinary extent as to lead to a copious eruption on the skin. 
But this eruption is nature's own conservative power ; her means of 
ridding the system of the poison which has grown within it. The 
vesicles which rise on the summit of the papidae cause their colour 
to change from red to white ; the scarf skin raised by an effusion 
of fluid beneath, constituting a sort of blister. Every one of 
these vesicles will yield that same morbific matter in a sensible 
form, which has entered into the organism in an unrecognisable 
form. It is, therefore, in this stage of the disease that we can obtain 
the material for any experimental purposes for which we may require 
it. In consequence, also, of the morbific matter being thrown out on 
the external surface of the body, the constitutional symptoms are con- 
siderably relieved. In the next or ulcerative stage, we observe that a 
great number of the vesicles burst, their contents are lost, and they 
dry into thick brown scabs. Some decline entirely, while others go 
on to ulceration. When animals reach this stage of the disease, we 
invariably find an increase of the constitutional symptoms ; for though 
in the vesicidar stage the disease is not fatal ; animals which have held 
out so far are almost certain to die if ulceration follows. According 
to the general strength of the animal's constitution, and the treatment 
and management observed towards it during its illness, we date from 
this time the recovery of the animal, but this is accompanied with 
