Report on the Bacteriology of Water. 517 



the typhoid bacilli were discovered on 28.10.1893, or eigJit days after 

 infection in the flask which was kept at rest, whilst they were not demon- 

 strable on the same day in the case of the flaslc which had been subjected 

 to agitation. 



In the unsterile Loch Katrine water, again, although on 

 7.11.1893 typhoid bacilli were found both in the water which had 

 been kept at rest and in that which had been agitated, yet the 

 broth-tube with five drops of the phenol solution only became turbid 

 in the case of the water which had remained at rest, thus tending to 

 show that the typhoid bacilli were more numerous or in a more active 

 condition in this latter water than in that which had been agitated. 



From the experiments made with the sterilised Thames, Katrine, 

 and deep well waters, it is evident that in none of these waters does 

 the typhoid bacillus proliferate, the longevity of the bacilli being 

 greatest in the Katrine and least in the deep-well water; on the 

 other hand, in the unsterilised waters their longevity is decidedly 

 greatest in the deep-well, and decidedly least in the Thames, water. 



In the sterilised water the principal factor determining longevity 

 would, therefore, appear to be the proportion of organic matter 

 present, which is much greater in the Loch Katrine and Thames than 

 in the deep well water ; on the other hand, in the unsterilised water 

 the factor determining longevity must be an entirely different one ; 

 and whatever it may be, it is more conspicuous in the case of the 

 two surface (Thames and Loch Katrine) than in that of the subter- 

 ranean (deep well) water. It is, as has already been frequently indi- 

 cated, generally believed that the more rapid disappearance of 

 pathogenic bacteria in unsterile than in sterile waters is due to the 

 multiplication or competition of the common water bacteria in the 

 unsterile waters ; but these experiments clearly show that this cannot 

 be true, at any rate without some qualification, for by reference to 

 the tables on pp. 495, 497, and 499. it will be seen that it was precisely 

 in the case of the deep well water that the most extensive multiplica- 

 tion of the water bacteria took place. In this connection it is 

 interesting to compare the following statement made by Professor 

 Ray Lankester, F.R.S., to the recent Royal Commission on the London 

 Water Supply (Appendix, p. 458) : 



"I took pure cultures of a very active and common fluviatile form, 

 B. jluorescens liquefaciens, which suggested, by its vigorous action on 

 gelatine, the possession of destructive properties. With this I mixed 

 a pure culture of Bacillus typhosus, and studied the mixed culture, 

 both by drop culture under the microscope and in the tube. During 

 a fortnight no diminution of the activity or numbers of either species 

 was observed. I have experimented with pure cultures of other 

 fluviatile species, and intend to continue the observations. It is 

 possible indeed not improbable that one or more species may be 



