QUALITATIVE BACTERIOLOGICAL ANALYSIS. 219 



obtained with two particular cultures of these organisms, and in 

 neutral peptone water. My own experiments showed that the 

 B. typhosus, when growing with B. coli maintained its power 

 of reacting to anti-typhoid serum so long as it could be isolated 

 from the mixture. Also experiments made at Netley on the 

 inter-action of B. coli and B. typhosus when planted out 

 in large quantities in tap- water, showed that even when em- 

 ploying Remy's medium B. typhosus could riot be isolated after 

 the thirteenth day. The colonies of B. coli acquired much the 

 same appearances as those of B. typhosus, so that it was necessary 

 to sub-culture all the colonies before a diagnosis could be made 

 between the two organisms. 



The whole question of the duration of life of the B. typhosus 

 in water and sewage is very complex ; temperature, the amount 

 of nutriment, the presence of other organisms and their toxines, 

 the number and vitality of the typhoid bacilli introduced, are 

 powerful factors which influence the result in various ways. In 

 most experiments the typhoid bacilli have been introduced in 

 considerable numbers, but examination of the stools of typhoid 

 patients has shown that typhoid bacilli may not be present in 

 any quantity when water is fouled by typhoid dejecta. Wathelet 

 only found ten colonies of B. typhosus among six hundred 

 colonies having characters common to B. coli and B. typhosus, 

 which he isolated from typhoid stools. Consequently it seems 

 extremely probable that under natural conditions comparatively 

 few typhoid bacilli will gain access to a water supply, and to 

 detect them it will be necessary to examine a considerable 

 quantity of the water. The bulk of the experimental evidence 

 seems to show that, unless the specific pollution is continuous, 

 it is extremely unlikely that typhoid bacilli will be detected in 

 a water if more than a week has elapsed since the actual pollu- 

 tion occurred. The outbreak of typhoid fever at Maidstone 

 affords considerable support to this view. Washbourn made a 

 bacteriological examination of the infected water about ten days 

 after the specific infection had taken place. He failed to find 

 the B. typhosus, though the presence of B. coli showed that 

 sewage contamination of the water had occurred. When, how- 

 ever, sewage containing the specific excreta passes into a cess- 

 pool, and percolates at once into the surrounding ground, the 



