368 THE TYPHOID BACILLUS 



animals die with the lesions of septicaemia. In monkeys and rabbits typical 

 attacks of enteric fever have been induced by feeding with typhoid bacilli. 



A. Inoculation of viruses of ordinary virulence. Even cultures which have 

 been sown with material direct from a case of enteric fever do not as a rule 

 lead to a generalized infection in the lower animals, though occasionally 

 guinea-pigs and mice can be infected by inoculating them in the peritoneal 

 cavity. Sub-cutaneous inoculation generally results in the formation of a 

 small abscess at the site of inoculation from which the animal rapidly recovers. 



In rabbits, guinea-pigs and dogs, intra-cranial inoculation of a small amount 

 (O05-O1 c.c.) of a fifteen- or twenty-day old culture gives rise, by reason of 

 the toxin it contains, to severe symptoms which terminate fatally. The 

 inoculation of young cultures produces nothing more than a transitory 

 illness (Vincent). 



B. Inoculation of viruses of exalted virulence. Sanarelli, Chantemesse and 

 Widal and others have succeeded in increasing the virulence of typhoid bacilli 

 and with these exalted viruses they can always be certain of producing a 

 typhoid septicaemia in laboratory animals. 



Methods of increasing virulence. (a) Sanarelli inoculated 5 c.c. of a 

 twenty-four-hour old broth culture of a typhoid bacillus of ordinary virulence 

 into the cellular tissue of a guinea-pig and at the same time into the peritoneal 

 cavity 10 c.c. of an old sterilized broth culture of the colon bacillus : death 

 supervened in about 20 hours and post mortem the typhoid bacillus was found 

 in the peritoneal cavity and occasionally also in the spleen and blood. 



A little of the peritoneal exudate from this animal was then sown on broth 

 and it was found that 5 c.c. of the broth culture sub-cutaneously inoculated 

 into a second guinea-pig would kill the animal if, at the same time, 7-8 c.c. 

 of a sterilized culture of the colon bacillus were inoculated intra-peritoneally. 

 By thus passing the bacillus through a series of animals diminishing at each 

 inoculation the dose of colon bacillus culture, it happened that after a short 

 time a strain of the typhoid bacillus was recovered which could, unaided by 

 the simultaneous inoculation of the colon bacillus, lead to an enteric infection 

 in rabbits and guinea-pigs when inoculated sub-cutaneously in doses of 5 c.c. 



Similar results were obtained by Sanarelli if instead of the colon bacillus he 

 inoculated sterilized cultures of Proteus vulgaris, sterilized cultures of stools, or an 

 infusion of meat a month old sterilized at 120 C. By simply feeding guinea-pigs 

 with small quantities of this infusion he was able to secure the generalization of a 

 typhoid bacillus which before had no pathogenicity for the guinea-pig. 



In the case of a virus which is fatal to guinea-pigs in large doses the viru- 

 lence may be raised by passage intra-peritoneally through guinea-pigs. For 

 this purpose 2 or 3 c.c. of a peritoneal exudate rich in bacilli are inoculated 

 in the first instance, then, as the virulence increases, as evidenced by the fact 

 that the animals die in a shorter space of time and by the diminished quantity 

 of exudate found post mortem, the quantity injected is gradually reduced to 

 0-5 and O'l c.c. After fifteen to twenty such passages a single drop is suffi- 

 cient to kill an adult guinea-pig in 12 hours. After the thirtieth passage the 

 virulence is fixed and cannot be further increased. A few drops of a twenty- 

 four-hour old broth culture of the " fixed virus " is sufficient to kill susceptible 

 animals on intra-peritoneal inoculation. If inoculated sub-cutaneously 

 much larger doses must, however, be employed : thus, for instance, in the 

 case of rabbits and guinea-pigs 1-4 c.c. and for mice 0'5 c.c. are necessary. 



Note. In attempting to raise the virulence of an organism by passage through the 

 peritoneal cavities of guinea-pigs it is important to utilize the peritoneal exudate 

 itself for the successive inoculations and not cultures sown from the exudates. To 



