HEMORRHAGIC SEPTICEMIA GROUP 301 



per cent, of phenol, then heated to 44 for three hours, then its 

 sterility determined by transfers to broth. If the broth shows no 

 growth, the material is sterile and is ready for use. This may 

 be used to inject laboratory animals and thereby establish im- 

 munity. The animal immediately after injection becomes more 

 susceptible to the disease, presumably due to the presence of ag- 

 gressin in the blood, but later a relatively permanent active im- 

 munity is produced. In practice it is found that in the immuniza- 

 tion of hogs it is necessary that the exudate containing the ag- 

 gressin be obtained from other hogs rather than rabbits. Wasser- 

 mann and Citron have developed a somewhat similar method of 

 immunization by the use of so-called " artificial aggressins " or 

 bacterial extracts. These methods of immunization are of much 

 more theoretic than practical importance. 



Passive immunization by means of antisera has been studied 

 by several investigators. A rabbit may be actively immunized 

 by one of the preceding methods, and its serum may protect a 

 mouse in doses of less than 0.1 c.c. against a fatal injection of a 

 highly virulent organism. Wassermann and Ostertag and their 

 pupils have shown that an antiserum specific for one strain of 

 B. suisepticus is not always effective for others. They, therefore, 

 prepare serum by the systematic immunization of a horse against 

 several strains of the organism until a serum of high potency 

 is produced. Its strength is determined by injections into mice. 

 Experiments upon young pigs with this serum are claimed to have 

 been highly successful, but the method has not come into general 

 use. Simultaneous injections of immune sera and of B. suisepti- 

 cus have also been advocated. 



In summary it may be said that immunization against swine 

 plague is still in the experimental stage, and that no completely 

 satisfactory method has been evolved. 



Bacteriologic Diagnosis. The identification of the causal 

 organism by actual isolation is the only practicable method of 

 bacteriologic diagnosis. 



Transmission. The means by which the disease spreads 

 naturally are not fully understood. It is possible that it is by 

 ingestion, prbbably sometimes by inhalation. 



