546 Profs. Percy Frankland and Marshall Ward. 



to great variations in the different experiments, doubtless largely in 

 consequence of the different initial vitality of the typhoid bacilli em- 

 ployed, and also, doubtless, in consequence of the different numbers 

 in which they were introduced in the several series of experiments. 



Of principal interest is the comparative experiment made with 

 Thames, Loch Katrine, and deep well water, in which typhoid bacilli 

 from one and the same source, and in the same numbers, were intro- 

 duced into these three types of water, and in which the duration of 

 life was found to be shortest in the Thames water (9 13 days), 

 longest in the deep well water (33 39 days), and intermediate iu 

 the Loch Katrine water (19 33 days). This result is of very great 

 practical importance as indicating the greater danger of typhoid 

 bacilli gaining access to deep well than to surface water. This 

 danger is, in actual practice, further enhanced by the fact that well 

 water is almost invariably consumed without storage, whilst surface- 

 waters are often stored for days or weeks, and in the case of upland 

 surface water the storage frequently extends over many months. 



The effect of temperature on the duration of life of the typhoid 

 bacillus was well illustrated in the series of experiments with Loch 

 Katrine water (4.7.1893), in which it was found that at 19 C. the 

 typhoid bacilli had already disappeared in 4 to 11 days, whilst 

 at 6 8 C. they were alive for upwards of 17 days in the same 

 water. 



The effect of agitation or rest on the typhoid bacilli in these waters 

 was not very pronounced, but the evidence on the whole, both in the 

 case of the sterilised and unsterilised waters, goes to show that the 

 agitation or aeration of the water is unfavourable to the typhoid 

 bacilli, and that in the unsterilised waters it occasions a more rapid 

 multiplication of the water bacteria. 



6. The greater bactericidal power of unsterilised than steam-steri- 

 lised surface waters is not apparently due to the multiplication of the 

 water bacteria in the unsterile waters, bringing about a competition 

 or " struggle for existence " between these aquatic forms and the 

 typhoid bacilli, but rather to the elaboration of products by these 

 aquatic bacteria (and very possibly also by other vegetable life 

 present in surface waters) which are inimical and prejudicial to the 

 welfare of the typhoid bacilli. 



Thus, in the typhoid-infected unsterilised deep well water an enor- 

 mously greater multiplication of the common water bacteria took 

 place than in the unsterile Thames and Loch Katrine waters ; yet, 

 notwithstanding the typhoid bacilli not only lived much longer in 

 this unsterile deep well water than in the unsterile Thames and Loch 

 Katrine waters, but there was practically no difference between the 

 duration of life of the typhoid bacilli in the sterile and unsterile deep 

 well water respectively. 



