444 THE BACILLUS OF TYPHOID FEVER. 



cultures appear 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 

 in it. The test is said to be still more reliable if 0.05 per cent of car- 

 bolic acid is added to the " potato-gelatin." According to Holz, the 

 addition of more than 0. 1 per cent of carbolic acid to nutrient gelatin 

 prevents the free development of the typhoid bacillus. 



Thoinot has claimed to be able to obtain the typhoid bacillus from 

 mixed cultures as, for example, from f^ces by suspending a small 

 amount of material containing it for several hours in a solution con- 

 taining 0.25 per cent of carbolic acid. While other bacilli are 

 destroyed, the typhoid bacillus is said to survive such exposure. 



The method of Parietti has been tested in a practical way by 

 Kamen, and proved to be satisfactory for the detection of the typhoid 

 bacillus in water which was supposed to be the source of a local 

 epidemic of the disease. The following solution is used : 



Carbolic acid, ........ 5 grammes. 



Hydrochloric acid (pure), 4 



Distilled water, 100 



