344 DISEASES OF SWINE 



ready to use. No addition of any kind is made to the virus that is 

 intended for hyperimmunizing purposes, and, where possible, it is 

 used within twenty-four hours after it has been drawn. 



The immune animal which is to be treated is then brought into 

 the hyperimmunizing room and prepared for the operation. In 

 selection of animals for use as immunes there are a few points that 

 should be kept in mind, as they will very much facilitate the work. 

 In the first place, animals selected for this purpose should prefer- 

 ably be of the long, rangy type. The bacon type of animal seems 

 to give a better serum, stands injecting and bleeding better, and 

 gives more serum per pound weight than those of the lard type. 

 Another desirable advantage for the immune hog is a rather heavy 

 ear with prominent veins. This is especially of importance where 

 the virus is to be injected by the intravenous method. A long tail 

 is another desirable feature, as this insures sufficient amount of tail 

 to allow of the numerous bleedings that are to follow. 



In addition to being immune from cholera, the hog to be in- 

 jected with virus should also be free from tuberculosis, as it would 

 be highly undesirable to send out a serum drawn from an animal 

 that was suffering from this disease. Such a serum would very 

 likely contain germs of tuberculosis, and its injection in a herd 

 could not be followed by other than bad results. The presence or 

 absence of tuberculosis in the immune animals can be readily tested 

 by means of the intradermal or skin test, injecting 1 or 2 drops 

 of tuberculin between the layers of the skin. On examination of 

 the injected spot twenty-four hours later a severe inflammatory 

 zone indicates presence of tuberculosis in the animal. 



Testing Immunity. — The immunity of the animals to cholera 

 can also be tested by placing them for several days in an infected 

 feed lot. This should always be done in the case of animals that 

 are bought as immunes, with a history of having passed through 

 an attack of cholera. In the case of those that are treated on the 

 place by means of the double treatment, they can be immediately 

 turned into an infected feed lot without any danger, and, if they re- 

 main well at the end of the three-week period which should elapse 

 between giving of the double treatment and hyperimmunization, 

 they may safely be regarded as suitable subjects for injection with 

 the large doses of virus. 



