BACTERIOLOGY OF WATER 227 



after pumping has been carried on for some time. A 

 sample from definite depths can be collected by small 

 vacuum bulbs, which are let down to the necessary depths 

 by means of a weighted wire or string; the drawn-out 

 point of the bulb is then broken by a suitable mechanical 

 arrangement (Sclavo's ' smash bottles '). If more than 

 three hours must elapse between sampling and com- 

 mencement of examination, the bottle must be kept or 

 packed in ice. 



Bacteriological Examination of Water. 



Although examination for a specific pathogenic organ- 

 ism is sometimes required, bacteriological examination 

 of water is generally directed at the demonstration of 

 absence or presence of sewage contamination. The 

 important water-borne diseases being usually of intestinal 

 origin, absence of sewage contamination shows fitness 

 for drinking purposes, unless of course chemical examina- 

 tion has shown metallic or other poison or excessive 

 mineral salts to be present. Of course, no examination 

 is a criterion of permanent fitness for use where inter- 

 mittent or sporadic pollution is possible. 



A bacteriological examination may fail to indicate a 

 dangerous water where urine, but not faecal, contamination 

 occurs. In such a water there may be a high count, 

 but the absence of intestinal organisms will probably 

 produce a favourable bacteriological opinion. This form 

 of contamination is not so rare as is usually supposed, 

 and epidemics have followed when typhoid bacilluria has 

 contributed to it (see p. 99). Colon bacilli and streptococci 

 will also be absent from water receiving drainage from a 

 disused cesspool. 



Bacteriological examination will also fail when water 

 has been heated, treated with antiseptics, or filtered, for 

 the purpose of misleading the bacteriologist. 



A scheme drawn up by the committee appointed by 

 the Royal Institute of Public Health is very generally 

 followed in this country, according to which the irreducible 

 minimum of procedures should be 



(a) Enumeration of bacteria capable of growth at room- 

 temperature (18 to 22 C.). (6) Identification and enumera- 

 tion of B. coli, if present. 



The majority of the committee recommend, in addition: 



