122 DISEASES OF SWINE 



has taken place on a farm it is important that the premises should 

 be thoroughly disinfected before other healthy animals are brought 

 on the farm and placed in these pens. I have frequently seen cases 

 where an outbreak of cholera had occurred on a farm and all the 

 animals had either died or been sold. The farmer then went to a 

 distance of several miles and bought healthy hogs, brought them 

 home, and turned them into these infected pens. Such a practice 

 is practically equivalent to signing the death warrant of the 

 newly purchased stock. 



The sick hogs previously upon the premises have left behind 

 them their virus-bearing discharges, and, unless the pen has 

 passed through a process of freezing during a severe winter season, 

 the newly arrived hogs will begin to show signs of being off feed 

 in a few days, and in about fifteen days will begin to die. 



It should be made an invariable rule to thoroughly clean up 

 all litter and refuse, such as corn cobs, wood, etc., and destroy 

 same by burning. Wallows should be drained out and thoroughly 

 cleaned and the entire pen disinfected before any new animals 

 are admitted to the premises. 



(24) Previous diseases from which the animal may have 

 suffered are often important factors in relation to its susceptibility 

 to cholera. 



Hogs which have once had the disease will rarely get a second 

 attack. In some cases they do, but it is the exception rather than 

 the rule. 



Brood sows that have been through the cholera are usually 

 highly prized by breeders, on account of the fact that it has been 

 noted that pigs born from these immune sows rarely are attacked 

 by the disease, at least until after weaning. This may be said 

 with equal positiveness in the case of pigs born from sows that 

 have been immunized against cholera by use of the serum-simul- 

 taneous treatment. Pigs in this class of herds are usually immune 

 from attack by the disease until after they have been weaned. 



This temporary immunity is no doubt due to the fact that there 

 is some substance contained in the milk of the mother which acts 

 as a protective agent in preventing the young from an attack of 

 the disease. 



Other diseases which may prove of importance in determining 



