136 Swine Plague. 



tion against pure swine plague docs not appear necessary, 

 because of its rather harmless character, vaccines prepared 

 from this organism could at best be considered as a probable 

 protection against the secondary infections of hog cholera, and 

 also perhaps to a certain degree as protective against the pneu- 

 monia of pigs depending on a mixed infection with the swine 

 plague organism. Nevertheless the numerous experiments for 

 the establishment of a method of vaccination which would pro- 

 tect against the infection with the bacillus suisepticus have a. 

 practical importance inasmuch as some of them, especially the 

 inoculation with immune sera against tJie so-called chronic 

 swine plague of pigs (see page 142), are extensively employed 

 in Germany. 



1. Active Immunization. In rabbits and guinea pigs this may be 

 attained with cultures killed at 58"' C. (iSniith & Moore), as well as with 

 the toxic substances isolated from the cultures (Suplagotoxin and Sapla- 

 goalbumin (see page 128), with which Schweinitz succeeded in pro- 

 tecting hogs against artificial infection. 



More recently Veil immunized hogs with an exudate (aggressin) 

 obtained from infected rabbits and hogs of which 10 cc. injected in 

 two parts or as one dose into the blood afforded a protection against 

 a lethal artificial infection. In order to protect the animals against 

 natural infection, w^iich is especially dangerous at the commencement 

 of the treatment, the simultaneous use of antiaggressive immune serum 

 is recommended. Similar favorable results were obtained by Citron 

 in rabbits and guinea pigs with exudate as well as with extracts from 

 cultures, and animals immunized by his method withstood a hundred 

 thousand times larger dose than that necessary for fatal infection. 

 Titze employed shake-extracts of filtrates made from cultures, and 

 recently Miessner & Schern used pleural exudate and heart blood from 

 rabbits containing aggressins and sterilized at 44*^0. with which 

 they produced an active immunity in guinea pigs against virulent 

 infection with swine plague bacteria. 



Beck & Koske produced an active immunity in pigs by injecting 

 them intraperitoneally first with 0.5 cc. of fresh bouillon culture heated 

 to 55° C. for 20 minutes, and seven days later with 1 cc. of virulent 

 culture into the muscles of the thigh. Broil, however, found that the 

 animals occasionally became fatally affected with peritonitis and enter- 

 itis as a result of the first infection, due to the poisonous toxic action 

 of the killed bacilli, and further that the vaccination in infected herds 

 favored the development of new cases before innnunity had been 

 established. 



According to Broil's experiments the administration of living fowl 

 cholera bacteria, or of such killed by heating for 20 hours at 52° to 

 55°C. does not produce a sufficient resistance against swine plague infec- 

 tion, whereas swine plague bacteria killed in a similar manner produced 

 in pigs a high grade of protection. The best results against artificial 

 infection were obtained with a 48-hour shake-extract prepared by the 

 method of Wassermann & Citron. The extract is not filtered, and is 

 sterilized by the addition of mustard oil. The vaccination of new 

 born pigs is recommended with such extract and immune serum (the 

 serum is supposed to prevent an infection during the negative phase), 



