PATHOGENIC BACTERIA IN WATER 53 



favourable a character as to destroy the vitality of seemingly more 

 hardy microbes — for example, the typhoid bacillus. The same 

 cannot be said for the B. coli test, since B. coH is a more hardy germ 

 than B. typhosus. 



Broadly, therefore, it will be seen that the presence of B. coli or 

 B. enteritidis sporogenes or Streptocoi'd in a water is presumptive 

 evidence of sewage pollution. But that in forining an opinion it is 

 essential to bear in mind the relative abundance of organisms per 

 c.c. and the relative abundance of certain species. 



(c) Pathogenic Bacteria in Water. — The two chief types of 

 disease-producing organisms found in water are the bacillus of 

 typhoid fever and the bacillus of cholera. These diseases and their 

 causal organisms are dealt with subsequently (see pp. 298 and 384). 

 Here it will only be necessary to note one or two general facts as to 

 the relation of pathogenic organisms to water supplies. 



In sterilised water, and in very highly polluted water or sewage, 

 pathogenic bacteria do not flourish. In the former case they die of 

 starvation, although there are experiments on record which appear 

 not to support this view ; in the latter case they are killed by the 

 enormous competition of common bacteria. Even in ordinary watei' 

 there is a wide divergence of behaviour. Some bacteria are destroyed 

 in a few hours ; others appear to flourish for weeks. In all cases the 

 spores are able to resist whatever injurious properties the water may 

 have much more persistently than the bacilli themselves. These 

 changes in the vitality of bacteria in water, partly due to the water 

 and partly to the other micro-organisms, bring about two character- 

 istics which it is important to remember, viz., that pathogenic germs 

 in water are, as a rule, scanty and intermittent. It is these features 

 in conjunction with the enormous quantities of common water bacteria 

 which make the search for the bacillus of typhoid fever what Klein has 

 called " searching for a needle in a rick of hay." Not that it cannot 

 be detected, but its detection is one of the most difficult of investiga- 

 tions. In recent years the typhoid bacillus has been isolated from 

 water which had given rise to cases of typhoid fever at Pierrefonds 

 (Widal & Chantemesse), Dijon (Vaillard), Chateaudun, Cuxhaven 

 (Dunbar), and possibly one or two other instances.* Undoubtedly 

 a large number of epidemics have been due to typhoid infected water, 

 but for obvious reasons (long incubation of typhoid, the fact that 

 the bacillus only lives in water for a few days, etc.), the cases where 

 the bacillus has been actually isolated are very few. In the Milroy 

 Lectures for 1902, Professor Corfield gives records of between 50 and 

 60 typhoid epidemics since 1864. We shall refer to this matter 

 subsequently when Bacillus typhosus is under consideration. 



In artificial cultivation water bacteria respond very readily to 

 * Brit. Med. Jour., 1900, ii. p. 1198. 



