PREDISPOSING CAUSES 123 



an outbreak of cholera on a farm are affections of the respiratory 

 and digestive tracts. The importance of intestinal worms has 

 already been mentioned, and in a general way what has been said 

 about worms holds good in the case of other conditions. 



Hogs which have been suffering from diarrhea, bronchitis, and 

 similar diseases are in poor condition to resist and overcome an 

 attack of cholera, and, accordingly, easily develop the disease 

 if it makes its appearance in a neighborhood. 



(25) Miscellaneous Factors. — In the preceding pages all the 

 important predisposing factors in causing an outbreak of cholera 

 and promoting its rapid spread have been discussed. There are 

 still a few minor points which may be mentioned. 



For instance, small rodent animals, such as rats, mice, wood- 

 chucks, squirrels, skunks, and rabbits, often carry the infective virus 

 hog-cholera from one farm to another. Rats particularly are fre- 

 quent inhabitants of hog yards, and these animals have a marked 

 tendency to migrate from one farm to another if food supply be- 

 comes low. By close association with the sick hogs and infected 

 premises they have ample opportunity to acquire and transmit 

 infection on their paws, bodies, and nests. 



On many farms more than one herd of hogs are kept, and the 

 herds may be in widely separated parts of the farm, but very fre- 

 quently the same person cares for, feeds, and waters both herds. 

 In such instances as these it can be very readily seen how easy it is 

 for the feeder to carry the infection on his boots or shoes from one 

 part of the farm to another. 



It should be made an invariable rule to always wash the shoes 

 or boots off thoroughly before going from one herd to another in a 

 different part of the farm, and especially so if there is any sign of 

 disease in either feed lot. 



Not infrequently in pastures located along the course of a large 

 railroad infection takes place in rather curious ways. Cars passing 

 over the railroad route carrying infected hogs invariably result 

 in the deposit along the roadbed of varying amounts of infected 

 manure and litter. This litter and manure, in the form of dust, 

 may be carried by wind over into the adjoining pastures, and form 

 the basis for an infection of the herds feeding in these fields. 



In other instances a railroad wreck may take place, and a large 



