THE AERTRYCKE BACILLUS 439 



Bainbridge and O'Brien are of opinion that the normal habitat of the organism 

 is the alimentary canal of pigs and perhaps of other domestic animals, and the 

 meat derived from such animals, but that in England such occurrence is rare. 



In many epidemics among pigs suffering from hog cholera the bacillus is present 

 in small numbers in the blood and in enormous numbers in the intestinal lesions, in 

 the juice of the lungs, in the bronchial mucus, urine, lymphatic glands, liver, spleen 

 and excreta. It is not infrequently accompanied in these cases by other micro- 

 organisms of secondary infection such as the colon bacillus. Swine become infected 

 by eating food contaminated with the excreta of infected animals. 



SECTION I. EXPERIMENTAL INFECTION. 



Guinea-pigs, rabbits, rats and mice are very susceptible to inoculation 

 with the aertrycke bacillus. 1 These animals may be infected by inoculating 

 them either beneath the skin, in the peritoneal cavity or in the muscles. 



Guinea-pigs. The bacillus is extremely pathogenic to guinea-pigs (Petrie 

 and O'Brien). Doses of O001 c.c. of a young broth culture invariably caused 

 the death of guinea-pigs weighing 250 grams in about 5 days : in some cases 

 doses of O000,l and 0'000,001 c.c. proved fatal. Guinea-pigs however are 

 not readily killed by feeding them with cultures of the bacillus. 



White rats. Doses of 2 c.c. of a young broth culture were fatal in 6 days 

 when given sub-cutaneously and 1 c.c. intra-peritoneally was fatal in 24 

 hours. 



Mice. Whether inoculated beneath the skin or into the peritoneal cavity 

 a dose of 0*01 c.c. of a young broth culture is fatal within 2 days. 



Rabbits. O'l c.c. of a young broth culture sub-cutaneously killed a rabbit 

 weighing 900 grams in 2 days, O'l c.c. intra-peritoneally was fatal to a 

 rabbit weighing 1300 grams in 24 hours, and 0*01 c.c. intra-venously killed a 

 rabbit weighing 1300 grams in 5. days (Petrie and O'Brien). 



Post mortem, the principal feature in acute cases is intense local haemor- 

 rhagic oedema, and in more chronic cases necrosis or abscess at the site of 

 inoculation : it is rare to find even minute spots in the liver and spleen in 

 experimental animals (Petrie and O'Brien). 2 



Pigeons are less susceptible to infection ; a fatal result can be obtained 

 only by using considerable doses and inoculating into the muscles or beneath 

 the skin. They cannot be infected by feeding. 



The virulence of the bacillus can be increased in a very extraordinary 

 manner by passing it through a series of pigeons. Selander, by passing a 

 virulent strain which had already been passed through several rabbits through 

 a series of pigeons, obtained a virus which was so highly virulent that 0*05 c.c. 

 of the blood of the pigeon when inoculated into the ear vein of a normal 

 rabbit killed the animal in 4 or 5 hours : the bacilli in the blood of this pigeon 

 were thirty times more numerous than the red cells. 



Swine. Swine are only slightly susceptible to sub-cutaneous inoculation 

 of cultures of standard virulence, and to overcome this insusceptibility a 

 virus the virulence of which has been increased by passing it through pigeons 

 must be used. Intra- venous inoculation is more severe and invariably 



1 A recently isolated strain must be used ; in culture the organism soon loses its 

 pathogenicity. 



2 These appearances may be compared with those found in two epizootics among 

 guinea-pigs, which the same observers attributed to a filter-passing organism but from 

 many of the animals affected with which the aertrycke bacillus was isolated. The 

 intestines of these animals were often congested ; the liver and spleen were usually con- 

 gested, and occasionally contained small grey or yellow nodules : in some of the cases 

 the supra-renals showed varying degrees of congestion, and patchy congested areas were 

 often seen in the lungs : effusions into the serous cavities did not occur. 



