8 HOG CHOLEBA 



Young pigs, especially those farrowed and 

 nursed by immune mothers, are often immune to 

 cholera during the first few weeks of life, and a 

 general impression that all pigs nursing immune 

 sows are likewise immune seems to have gained 

 ground. This impression is not in accord with 

 the facts, for we have seen individual pigs born of 

 immune mothers and suckled by them, dead of 

 hog cholera on the seventh day following birth, 

 and under like conditions of birth and sustenance 

 we have frequently seen entire litters succumb to 

 the disease before attaining an age of four weeks. 

 Among older hogs raised in localities where hog 

 cholera is not prevalent, the " natural immunes" 

 so frequently mentioned are by no means common, 

 and it is probable that in places where they are 

 found in considerable numbers they owe their im- 

 munity to the fact that they are exposed to cholera 

 as young pigs, and suffering only a slight reac- 

 tion, are rendered immune. As a general rule, 

 young shoats, old hogs, and sucking pigs are most 

 susceptible to cholera in the order named, and, as 

 would be expected, recoveries from the disease 

 are less frequent among young shoats, and more 

 frequent among old sows and sucking pigs. 



The cause of hog cholera is a filterable virus, 

 probably an organism too small to be visible with 

 the highest magnification now obtainable, and pos- 

 sibly possessed of characteristics which prevent it 



