286 THE BACILLUS OF SWINE ERYSIPELAS 



woolly-looking and the centre of the colony forms a small brownish 

 spot. 



Agar. At first the growth is similar to that on gelatin, but it soon assumes 

 an homogeneous appearance and forms a delicate 

 scanty layer. 



Potato. On potato the organism only grows under 

 anaerobic conditions and then forms a barely visible 

 streak. 



SECTION III. BIOLOGICAL PROPERTIES. 

 1. Vitality and virulence. 



The bacillus of swine erysipelas remains alive for 



FIG. 185. Bacillus of swine several months in cultures under anaerobic conditions, 

 SatufSo (I dlys) COl ny n an( l shows an equal vitality in deep stab cultures in 

 ordinary gelatin : it will give rise to sub-cultures 

 and even kill pigeons after 6 months. 



In aerobic broth cultures kept in the warm (37-39 C.) incubator the 

 virulence as well as the vitality vanish much more rapidly. The virulence 

 becomes progressively enfeebled and after about 20 days the culture is harm- 

 less. As already pointed out the virulence of an attenuated virus can be 

 restored by passage through pigeons. 



2. Vaccination. 



One attack of the acute disease confers immunity on swine ; moreover 

 an attack of the chronic form (Gout) protects an animal from the acute disease. 

 Pasteur and Thuillier considered it possible to immunize animals by inoculating 

 them with attenuated viruses, and at the present time vaccination of swine 

 is very extensively practised, especially in Austria. 



For the purposes of vaccination broth cultures which have been attenuated 

 (through the action of the oxygen of the air) by incubation for a longer or 

 shorter time in the warm incubator may be utilized. 



The pigs are inoculated first with a very weak virus, and then with a virus 

 which has not been in the incubator so long and which is therefore somewhat 

 more virulent. Pigs should be inoculated before they are 4 months old as 

 they are then less susceptible to the disease. The immunity so conferred, 

 which is complete 12 days after the second inoculation, lasts about a year, 

 and this is a sufficient length of time for fattening purposes. If the animal 

 is to be kept for breeding it is well to repeat the vaccination at the end of a 

 year. 



As stated above, the organism may also be attenuated for the pig by passage 

 through rabbits. After several passages the virus becomes very virulent for rabbits, 

 but attenuated for swine, and may then be used for inoculation as a vaccine. For 

 this purpose a tube of broth is sown with the spleen of the last rabbit of the series 

 and incubated, and the pig is vaccinated with the culture. 



3. Soluble products. Serum therapy. 



(i) Negative results follow the injection of filtered cultures. The amount 

 of growth, as has already been pointed out, always remains very scanty and 

 toxins are not formed in any appreciable quantity. But if rabbits be inocu- 

 lated sub-cutaneously with small quantities of unfiltered cultures they 

 quickly recover, and it soon becomes possible to inoculate large doses into the 

 veins without producing any morbid symptoms. Emmerich, Leclainche 

 and others killed rabbits which had been treated in this manner, made an 



