THE COLON-TYPHOID GROUP gg 



many cases infection has been traced to water which 

 chemical analysis showed to be of considerable organic 

 purity. Even bacteriological examination in which colon 

 bacilli and streptococci have been estimated will not 

 necessarily reveal danger from typhoid. Where a pre- 

 viously pure water is contaminated with urine from a 

 typhoid carrier, typhoid bacilli will be present without 

 colon bacilli and streptococci. Therefore, while as a rule 

 the ' bacterial indicators of pollution ' (normal intestinal 

 inhabitants) are to be found in a typhoid- bearing water, 

 it does not follow that because they are absent, typhoid 

 bacilli are also absent. 



Bacteria are not evenly distributed through the bulk 

 in unfiltered water, many being aggregated in masses, 

 so that where typhoid infection is present some of the 

 bacilli will be discrete, but very many will clump together. 

 Consumers of this water only imbibing separated bacilli 

 are not likely, or are less likely, to acquire the disease. 

 But the consumer who receives a clump of typhoid bacilli 

 is the less likely to resist infection (spotted distribution). 

 Storage and filtration, Houston believes, remove all likely 

 danger from aggregated microbes, and tend to render 

 separated microbes fairly equally distributed throughout 

 a water supply. 



There is no" ground for the suggestion that B. coli may 

 become transformed into the typhoid bacillus. The 

 persistence of the typhoid bacillus in water is largely 

 governed by the chemical constitution and bacteriological 

 characters of the medium (see also p. 225). 



Typhoid bacilli persist longer in bacterially pure waters 

 than in waters containing large numbers of bacteria, 

 and Houston has shown that raw river water infected 

 with ' uncultivated ' typhoid bacilli from a case of typhoid 

 bacilluria cleared itself of 99-99 per cent, of typhoid bacilli 

 after a week, and apparently the organism had completely 

 disappeared in ten days (cf. pp. 202, 211, 225). 



When they are present, infusoria and crustacean 

 organisms devour typhoid bacilli. Whipple and Mayer 

 found that in water kept under anaerobic conditions 

 (atmosphere of hydrogen) typhoid bacilli quickly died, 

 although under similar conditions it may thrive in nutrient 

 media. Houston found that between and 18 C., the 

 higher the temperature the quicker was the disappearance 



