229 DISEASES OF THE HOG. 
them all off. It is generally admitted that large 
herds of animals kept together are more liable to 
disease than when only a few are kept in the same 
place, and I think there is some truth in it, but it 
does not hold good in hog cholera, as it will make 
its appearance in all sorts and conditions of hogs 
(the “land pike” excepted). The reason, no doubt, 
why it does not usually kill all in a herd is that 
some have more resisting power or that they in 
some way become immune to the action of the bac- 
teria. Swine plague is just as fatal a disease as 
hog cholera and both may be present in the same 
outbreak. The symptoms of the disease are nearly 
the same and it is only by the use of the microscope 
that the difference can be ascertained (figs. 18 and 
19); but it is of little importance to the swine grow- 
er whether it is hog cholera or swine plague, as the 
management of both diseases are alike. It is said 
that hogs which have resisted an attack are im- 
mune from future attacks; this may be so in some 
cases, but not in all, as I have known hogs in a 
herd of swine attacked with hog cholera, a few of 
which escaped but were attacked the following 
year and died. Another peculiarity of hog cholera 
and swine plague is that some years it is much 
more virulent than others, sometimes destroying 
ninety to one hundred per cent; at others it may 
not amount to more than twenty to thirty per cent. © 
The first of the outbreak is always the most se- 
vere; towards the end the majority attacked re- . 
cover. 
