CHAPTER I. 



COLLECTION OF WATER. 



OPINION as to the value of a bacteriological examination of 

 water has passed through many phases. The elaboration of 

 Koch's gelatine plate method gave a great impetus to the 

 bacteriological study of water supplies ; it enabled an estimate 

 to be made of the number of micro-organisms present in a 

 given quantity of water, and so permitted a comparative study 

 of various sources of supply. It was at first assumed that from 

 the number of bacteria found in a water distinct evidence of 

 purity or contamination could be at once deduced. Further 

 investigations, however, soon showed that water organisms were 

 capable of multiplying enormously within a very short time, 

 and waters of great organic purity, under certain conditions, 

 might be found teeming with bacterial life. It thus became 

 evident that, though a paucity of organisms might indicate a 

 condition of purity, it did not necessarily follow that a large 

 number of micro-organisms pointed to contamination. Realising 

 that the mere enumeration of the bacteria present in a sample 

 of water was surrounded by many fallacies and, unless performed 

 under the strictest conditions, might give rise to false con- 

 clusions, bacteriologists turned their attention to the study of 

 the kinds or species of bacteria, and attempts were made to 

 distinguish between the microbes normally present in a water 

 and those derived from sewage i.e.., to distinguish between 

 water-organisms and sewage-organisms. 



The qualitative bacteriological examination, though un- 

 doubtedly of the first importance and likely in the long run to 

 be of the greatest practical value to hygienists, has been found 

 to be attended with exceptional difficulties. In the early days 

 of the study of bacteriology, and when modern methods of 



