Sterilisation Experiments on the Cambridge Water. 561 



becoming clear and bright, the redaction in the number of the 

 Bacillus coli was not up to the standard given above, a single 

 organism being found sometimes in 10 c.c, sometimes in 20 c.c. 

 and sometimes in 30 c.c. For all practical purposes, however, this 

 was sufficient, for, on examining bacterioscopically the water that 

 had been treated in a de Frise tower by ozone produced in a 

 Siemens-Halske generating apparatus*, 500 c.c. contained not a 

 single Bacillus coli. It is evident then that in ozonisation we 

 have a sterilising method which, applied to the Cambridge water, 

 will probably give excellent results. In order to obtain complete 

 sterilisation a low amount of organic matter and a small number 

 of organisms seemed to be essential as, on adding organic matter 

 and increasing the amount of Bacillus coli the quantity of ozone 

 required to bring about sterilisation seemed to increase out of all 

 proportion to the amount of these substances added. In con- 

 nection with this it should be remembered that when we speak 

 of sterilisation of water we refer to the destruction of disease- 

 producing germs or of organisms that are usually found alongside 

 such disease-producing germs. Sporebearing organisms need not, 

 here, be taken into account, as the presence of the sporebearing 

 organisms usually found in water affords no indication of the 

 presence of dangerous contamination. Streptococci and the Ba- 

 cillus coli communis, especially the latter, are the indicators we 

 search for as affording evidence of a possibly dangerous con- 

 tamination, whilst any method of sterilisation that will effectually 

 destroy these may be relied upon to destroy equally, or more, 

 easily any of the disease-producing organisms such as the typhoid 

 bacillus or the cholera bacillus that may have gained access to 

 the water supply. 



The Cambridge water is quite clear, contains a very small 

 quantity of organic matter, and the number of organisms is 

 exceedingly low, much lower indeed than in the majority of the 

 water supplies in the United Kingdom ; it is therefore an excel- 

 lent water on which to try the various processes of sterilisation. 

 From the sentimental point of view there seemed to be no 

 objection to the treatment of any water by ozone ; even those 

 who object to the addition of chemicals to water would probably 

 not object to the addition of the "health-giving" ozone. I mention 

 this at this point because, curiously enough, when we came to 

 consider the next method we found that certain waters con- 

 taining organic matter acquired a peculiar taste when treated 

 with chlorine and at first we supposed that this was something 

 specially associated with the taste of chlorine. When, however, 



* See de Frise, Sterilisation de I'eau par Vozone, 1907; Daske, Deutsche 

 Vierteljahrzcshr. f. bffentl. Gesundheitspflege, Braunschweig, Bd. 41, 1909, for 

 description. 



