486 Profs. Percy Franklaiid and Marshall Ward. 



It is in. this way that particular interest attaches to a comparison 

 of the results obtained by gelatine plate and phenol broth-cultur-e in 

 the case of these infected sterile waters, as the two methods can be 

 made to control each other, whilst in the case of the infected un- 

 sterilised waters the method of phenol broth-culture has to be exclu- 

 sively relied on for the detection of the typhoid and coli bacilli. 



Behaviour of tlie Typhoid Bacillus in the Loch Katrine Water. 

 (Second Series of Experiments.) 



In the first series of experiments with the L. Katrine water re- 

 corded above, the number of typhoid bacilli initially introduced was 

 so small that it would obviously not be possible to directly compare 

 the results with those previously obtained with Thames water in 

 which a much larger number of typhoid bacilli were initially intro- 

 duced, as I have found in previous investigations of the same kind 

 that one of the factors determining the longevity of pathogenic 

 bacteria placed in water, or for the matter of that placed in any un- 

 favourable surroundings, is the absolute number in which they are 

 present. In other words, amongst, for instance, 1,000 bacteria taken 

 from a given source there may be some individuals which will resist a 

 particular adverse influence, whilst amongst 10 bacteria taken from 

 the same source there may be none capable of resisting the adverse 

 influence in question. 



When, therefore, I found that such a small number of typhoid 

 bacilli had been introduced into the L. Katrine water in the first 

 series of experiments, I immediately started a second series of ex- 

 periments with the same water, but introducing a much larger 

 number of typhoid bacilli. 



In this second series of Loch Katrine experiments, which were 

 begun on 7.7.1893, or three days after the first, only unsterilised 

 Loch Katrine water was infected with typhoid, thus : 



Infection of J/. Katrine Water in Second Series of Experiments. 

 25 needle-loops were taken from the surface of an agar-culture of the 

 typhoid bacillus, 11 days old, and introduced into 20 c.c. of steam- 

 sterilised tap-water, which was then violently shaken for 15 minutes ; 

 10 c.c. of this water-attenuation were then added to 1500 c.c. of 

 unsterilised L. Katrine water. After thorough mixture this was 

 divided up amongst a number of sterilised flasks plugged with sterile 

 cotton-wool, which were placed in the incubator (19 C.) and re- 

 frigerator (6 8 C.) respectively. Control flasks containing the 

 same unsterilised L. Katrine water, but uninfected, were placed 

 under precisely similar conditions. 



The results of bacteriological examination of the uninfecied control 

 L. Katrine water are given in the following table : 



