222 DISEASES Ot^ THE HOd. 



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 trnth 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 powder 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 niucli 

 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 alv/ays the most se- 

 vere; towards the end the majority attacked re- 

 cover. 



