DETECTION OF PATHOGENIC BACTERIA IN WATER 275 



has hardly any effect upon the B. coli communis, which 

 develop almost as freely as on the control plate. Thus, 

 in the investigation of samples of water for typhoid 

 bacilli in which the determination of the number of the 

 latter is not desired, and in which there is a probability 

 of many liquefying organisms being present, such an 

 addition may prove of much service, and may therefore 

 be recommended, but it will not, of course, separate the 

 typhoid from the B. coli communis. 



Thoinofs Method. 1 This consists in adding 0*25 

 gramme of pure phenol to 100 c.c. of the sample of water 

 to be investigated. But an addition of O'llG per cent, 

 of carbolic acid greatly interferes with the growth of 

 the typhoid bacillus, whilst it will not develop at all in 

 the presence of 0*144 per cent. (Dunbar, loc. cit., p. 491.) 



It will thus be seen that there is at present no 

 method whatever of isolating the typhoid bacillus 

 from .water which does not at the same time also 

 isolate the B. coli communis, if the latter is present, 

 as it almost invariably will be, for all circumstances 

 hitherto examined which favour the growth of the 

 typhoid bacillus relatively to that of other bacteria are 

 equally or even more conducive to the growth of the 

 B, coli communis, and no agency is available for the 

 destruction of the B. coli communis which does not also 

 destroy the vitality of the typhoid bacillus. By the 

 judicious application, however, of some of the above 

 methods there can be no doubt that the discovery of 

 the typhoid bacillus is greatly facilitated. 



Thus, the water should be preliminarily purified 

 from most bacteria by culture in phenol-broth (pre- 

 ferably as in Parietti's method). On subsequent plate- 

 cultivation the colonies obtained will be limited to those 

 of B. coli cOmmunis, the typhoid bacillus, and possibly 



1 Gazette des Hopitaux, 1887, p. 348. 



T 2 



