492 Profs. Percy Frankland and Marshall Ward. 



Thus ivhen the typhoid bacilli were introduced into the L. Katrine 

 water in large numbers, they were still easily discoverable by phenol broth- 

 culture on the fourteenth day, although from the eliminations by plate- 

 cultivation {see p. 488) it is obvious that their numbets had undergone 

 enormous diminution. They doubtless persisted even longer than this, but 

 the experiments had to be interrupted. Thus when introduced in large 

 numbers their persistence is greater than when only small numbers are 

 employed, for in the previous experiments they were no more demonstr- 

 able in the unsterilised water ivhich had been Jcept at a summer tempera- 

 ture (19 (7.) for 11 days (seep, 476). 



COMIARATIVE BEHAVIOUR OP THE TYPHOID BACILLUS IN THAMES, 

 LOCH KATRINE, AND DEEP WELL WATEK. 



The previous experiments had clearly shown that the typhoid 

 bacillus, although unable to multiply in either ordinary Thames or 

 L. Katrine water, even when these waters are deprived of other 

 competing or inimical bacteria, is yet able to remain alive for con- 

 siderable periods of time in these waters, not onty when they are 

 previously sterilised, but even, although for a distinctly shorter 

 period, in their unsterilised condition and in the presence of an 

 abundant bacterial population. 



Inasmuch as the access of typhoid bacilli to potable water of all 

 kinds is one of the most ever-present dangers to the public health, 

 it becomes a matter of pressing hygienic importance to determine 

 whether the particular kind of water into which they may gain access 

 affects the chance of their reaching the water-consumer in a living 

 state. The population of the United Kingdom is chiefly supplied 

 with one or other of three different kinds of water, of which the 

 Thames, L. Katrine, and deep-well water of the Kent Company may 

 be taken as types, and it is with these three types of water that I 

 have, therefore, instituted the comparison in question. 



From the experiments which I have detailed above, it is obvious 

 that the longevity of the typhoid bacillus in any particular water is 

 subject to very considerable variations, according to the initial 

 vitality of the typhoid bacillus employed, and according as a rela- 

 tively large or small number of the bacilli is introduced into the 

 water. In order, therefore, to institute a comparison between several 

 different waters as to their relative capacity of maintaining the 

 typhoid bacilli in a living state, it is absolutely essential that the 

 typhoid bacilli placed in the several waters should be taken from one 

 and the same cultivation, and that they should be introduced in each 

 case in as far as possible the same numbers. 



These were the conditions which were secured in the series of com- 

 pnrative experiments made with these three different types of water, 

 and which are now to be described. 



