on the Baet&nology of Water. 547 



Of course it may be urged that, the unsterile deep well water 

 possibly does not contain those water bacteria which are particularly- 

 fitted for entering into successful competition with the typhoid bacilli, 

 and that perhaps such water bacteria are only to be found in the 

 unsterile surface waters. 



7. The series of experiments summarised in the following table 

 show that unsterile surface water, like that of the Thames, possesses 

 bactericidal powers irrespectively of any further multiplication of its 

 contained water bacteria, thus : 



Uninfected unsterilised Thames water, kept at 9 12 C., exhibited 

 but little change in the number of its contained bacteria over the 

 period of five weeks from 16.1.1894 to 24.2.1894. (The numbers 

 only varied from 5500 2825 per 1 c.c.) 



The same unsterilised Thames water, infected with about 170,000 

 typhoid bacilli per 1 c.c., exhibited a continuous decline in the total 

 number of. bacteria present in it over the same period. 



The same Thames water, after sterilisation by steam, was infected 

 with upwards of 100,000 typhoid bacilli per 1 c.c., and at the end of 

 the same period (16.1.1894 24.2.1894) there were still upwards of 

 5000 typhoid bacilli per 1 c.c. present. 



The same typhoid-infected steam-sterilised water was inoculated 

 with a few drops of unsterile Thames water to communicate to it the 

 Thames- water bacteria, and the latter underwent very extensive 

 multiplication in this water. Notwithstanding, the typhoid bacilli 

 lived between thirty-four and forty-one days in this water, whilst in 

 the unsterile Thames water, in which no multiplication of the water 

 bacteria took place, they only lived between twenty and twenty-seven 

 days. 



This shorter duration of life of the typhoid bacilli in naturally 

 unsterile Thames water than in that rendered unsterile by inoculation 

 I attribute to the circumstance that in the naturally unsterile Thames 

 water countless generations of water bacteria must have flourished 

 before the water is made the subject of experiment at all, and it 

 must, therefore, be more or less saturated with those bacterial 

 products which are prejudicial to the vitality of the typhoid bacillus, 

 and which, in fact, frequently hamper or even inhibit the further 

 multiplication of the water bacteria themselves. 



Thus it is obvious that the unsterile water in question was already, 

 at the outset of the experiment, in such a condition as to prevent any 

 multiplication of its own water bacteria, whilst, after it had been 

 steam sterilised, the same bacteria multiplied abundantly in it. But 

 again, at the outset of the experiment the unsterile water was in such 

 a condition as to cause a comparatively rapid disappearance of the 

 introduced typhoid bacilli, whilst after steam sterilisation it only 

 became again endowed with this power of destroying the typhoid 



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