THE BACILLUS OF TYPHOID FEVER. 353 



they also show thai the animals experimented upon frequently re- 

 covered after comparatively large doses, and that the typhoid bacil- 

 lus is not pathogenic in the same sense as are those microorganisms 

 which, when introduced into the body of a susceptible animal in very 

 minute amount, give rise to general infection and death. On the 

 other hand, a fatal result depends upon the quantity of the culture 

 introduced in the first instance, rather than upon the multiplication 

 of the bacillus in the body of the inoculated animal. This view is 

 confirmed by the experiments of Sirotinin, which show not only that 

 a fatal result depends upon the quantity injected, but also that a 

 similar result follows the injection of cultures which have been ster- 

 ilized by heat or filtration. The pathogenic action, then, depends 

 upon the presence of toxic substances produced during the growth of 

 the bacillus in artificial culture media. The researches of Brieger, 

 heretofore referred to, show the presence in such cultures of a toxic 

 ptomaine his typhotoxine to which the pathogenic potency of these 

 cultures appears to be due. White mice and guinea-pigs usually die 

 in from twenty-four to forty-eight hours when inoculated in the 

 cavity of the abdomen with a virulent culture of the typhoid bacillus 

 0. 1 cubic centimetre to 0. 5 cubic centimetre of a bouillon culture 

 three days old. According to Kitasato, the virulence of cultures 

 from different cases of typhoid fever varies considerably. 



Detection of the Typhoid Bacillus in Water. The generally 

 recognized fact that typhoid fever is usually contracted by drink- 

 ing water contaminated by the typhoid bacillus has led to numer- 

 ous researches having for their object the discovery of a reliable 

 method of detecting this bacillus when present in water in compara- 

 tively small numbers in association with the ordinary water bacilli. 

 The use of Koch's plate method, as commonly employed, will 

 not suffice, because the water bacilli present grow more rapidly 

 and cause liquefaction of the gelatin before visible colonies of the 

 typhoid bacillus are formed ; and, owing to the relatively small 

 number of typhoid bacilli, these are likely to escape detection. The 

 aim of bacteriologists has, therefore, been to restrain the growth of 

 these common water bacilli by some agent which does not at the 

 same time prevent the development of the typhoid bacillus. Chan- 

 temesse and Widal were the first to propose the use of carbolic acid 

 for this purpose. They recommended the addition of 0. 25 per cent 

 of this agent to nutrient gelatin ; but, according to Kitasato, the de 

 velopment of the typhoid bacillus is restrained by an amount exceed- 

 ing 0.20 per cent. 



Holz prepares an acid medium by adding gelatin (ten per cent) to 

 the juice of raw potatoes, and asserts that while the typhoid bacillus 

 grows luxuriantly in this medium, many other bacilli fail to develop 

 27* 



