156 DISEASES OF SWINE 



to begin with, that we get a short incubation period. In some cases 

 of this kind the symptoms of disease show up very quickly, and it 

 is sometimes possible to note signs of sickness within three or four 

 days after exposure. It is quite unusual, however, to have many 

 cases where the cholera symptoms are plain before the fifth day. 



The amount of virus or germs which enter the body of the 

 animal is also a most important matter in causing symptoms of 

 sickness to appear rapidly or later on. If there is only a small 

 amount of exposure, as from scattering of virus in the feed lot 

 from the feet of a commission man or hog buyer, who may be riding 

 about the country going from one feed lot to another without 

 properly cleaning his shoes, and carrying manure and mud from 

 feed lots where there are sick hogs to other pens in which the hogs 

 are still healthy, it will take longer for the animals to get sick. 

 In these cases there is only a very small amount of virus present, 

 and it will take quite a while for the germs to multiply in large 

 enough numbers to make the animals sick. 



On the other hand, if we have hogs that are shipped in cars 

 which have been used for shipping cholera hors, and have in this 

 way been infected, we will not have to wait long for signs of the 

 disease to appear. This also is true in cases where healthy hogs 

 are fed with the dead bodies of hogs which have died of cholera. 

 In such cases as these the well hogs take into their bodies a large 

 amount of disease-producing virus, and it takes only a short time 

 for them to get sick. 



Another way by which hogs may get the disease and get sick 

 very quickly is by placing them in pens that have been occupied by 

 cholera hogs only a short time before. For instance, if a farmer 

 buys a drove of healthy shoats at a public sale, and brings them 

 home and places them in pens or a feed lot in which he has lost 

 hogs from cholera a few weeks or months before, it is very likely 

 that these new hogs will get sick before he has had them on the 

 place a week. The reason for this is that the pens have been 

 filled with virus from the manure and urine of the animals which 

 died there, and the germs are present in large numbers ready to 

 attack any healthy hogs that may come into the lot. 



Vinilency of the Germs. — ^In some years the virus of cholera 

 seems to be very much more severe, and makes a much more rapid 



