THE EXAMINATION OF WATER . 641 



To Collect the Sample. 



Use sterile glass-stoppered bottles and immerse in the water 

 12 in. below the surface before removing the stopper. 



If from a tap, let it run for five minutes before taking sample. 



Remember that a local cistern contamination gives a fallacy not to 

 be applied to the water supply in general. 



For deep wells Sclaver's "smash" bottles should be used. 



These are small vacuum bulbs, let down by a string and 

 mechanically broken when under water. 



Examine the sample within three hours or pack it in ice. 



To Examine the Sample. 



Until recently bacteriological examinations of water supplies in 

 tropical countries have been few and far between, owing to the lack 

 of well equipped laboratories. When sufificient statistics are 10 hand 

 we shall be able to appreciate the difference of the bacterial content of 

 tropical waters and to modify existing standards of bacterial impurity. 



To one already accjuainted witli the subject in a temperate climate 

 there will appear dilficulties innumerable. He will find that standards 

 of impurity cannot be applied generally and that the local water con- 

 ditions vary enormously. 



For example in the tropics : — 



(i) The rains are torrential and periodic, so that the bacterial flora 



of districts where vegetation is rank will be brought down. 



The surface organisms of sandy districts, where much vegetation 



is absent, mav give an altogether different flora from the 



above. 



(2) The sun and soil kill off all the H. coli communis, where it has 



existed, but other resistant types persist, new probably to the 

 sanitary worker. Their significance as infectious and danger- 

 ous agents in water supplies has to be ascertained. 



(3) A clay subsoil, instead of acting as a lifter in purifying the 



water, in some measure may provide a culture media for its 

 increased pollution, oAving to the organisms being held up, 

 cultured, and swept away into surface waters during the first 

 shower. 



(4) The sanitarian will be frequently called upon to deal with the 



bacteria persisting after the action of sun and soil, which 

 residual bacteria may not include the notorious B. coli com- 

 munis, the presence of which forms a basis for a standard of 

 impuritv in temperate countries. 



(5) Animals residing in a catchment area will give a very distinct 



bacterial flora from that in temperate climates where the 

 pollution is largelv from human fcccal bacteria from the large 

 towns on the river banks. 



