ADDENDUM 183 



may be purified at a reasonable cost, so as to yield no B. coli 

 in 100 c.c. in the majority (about 75 per cent.) of samples 

 examined. 



" It is much more difficult to suggest a standard by which a 

 water should be condemned. All that the Committee feel 

 justified in stating is that the further a water departs from the 

 above standard of purity (no ' lactose -f indol 4- ' B. coli in 

 100 c.c.) the greater is the suspicion attaching to it, unless the 

 local conditions and circumstances are such as to exclude 

 undesirable pollution." 



3. Water in Swimming Baths. 



The bacteriological content of the water in swimming baths 

 has been in recent years made the subject of a number of 

 investigations. It is a matter of some importance since a not 

 inconsiderable quantity of water is swallowed by bathers, 

 while in this and other ways it is obvious that infection may be 

 spread. 



In a number of cases outbreaks of infectious disease, such as 

 typhoid fever, dysentery, Weil's disease, trachoma and infectious 

 conjunctivitis have been definitely ascribed to bathing in con- 

 taminated rivers or in public swimming baths. 



The methods of examination are similar to those employed 

 for drinking water except that since the contamination may be 

 considerable, dilution methods must be practised and amounts 

 as small as O'Oi, cxooi c.c., etc., may have to be examined for 

 B. colt, number of bacilli, etc. 



It is obvious that the bacteriological results will vary very 

 greatly with the local conditions, and no standards of permissible 

 numbers can be as yet satisfactorily laid down. The chief local 

 conditions affecting the bacterial content are the volume of water 

 in relation to the number of users, the frequency with which the 

 water is changed, the character of the users as regards personal 

 cleanliness, the initial purity of the water, the temperature of the 

 water and the local conditions of the examination (i.e. time of 

 examination in relation to freshness of the water). 



A few particulars of investigations will serve to illustrate the 

 kind of findings met with. 



