DIAGNOSIS, DIFFEBENTIAL DIAGNOSIS, PROGNOSIS 59 



4. Animal Inoculation (rarely applicable). 



History. Securing the history of an outbreak 

 of suspected hog cholera is simply applying knowl- 

 edge of the ways in which the virus spreads. 

 Usually we find that a hog has died of an unknown 

 cause and. a few days later sickness has appeared 

 among its associates. Careful inquiry should be 

 made regarding recent introduction of hogs into 

 the herd, existence of swine disease in the vicinity, 

 adjacent arteries of traffic and source of feed and 

 water supply. Stockyard hogs and others intro- 

 duced without clear history of previous health 

 should remain under suspicion. Even though 

 they do not themselves contract the disease they 

 may act as intermediate carriers. There is no 

 evidence that hog cholera virus travels through 

 the air but a road or railroad right-of-way may be 

 contaminated by the drip from infected wagons or 

 cars. If the herd is subsisting on garbage and is 

 not immune the circumstances suggest hog chol- 

 era. If kitchen swill is being fed inquiry should 

 be made as to whether the kitchen is supplied with 

 market pork. 1 



In general the facts brought out by the history 

 of an outbreak simply constitute supplementary 



1 In one instance that came under our observation an outbreak 

 of hog cholera was traced to meat trimmings that were placed in 

 a poultry house. Two small pigs formed the habit of escaping 

 from the pen and eating freely of these trimmings. Both devel- 

 oped hog cholera simultaneously, and later transmitted it to their 

 associates. 



