BACTERIAL CONTENTS OF VARIOUS WATERS 105 



Bacterial Composition of Well-water before, and after Disturbance 



(Rubner) 



Buhner, in . pointing out the enormous increase in 

 the number of bacteria after disturbance of the sediment, 

 states that the well had only been made from a half to 

 three-quarters of a year previous, and had been so care- 

 fully constructed that no external pollution could pos- 

 sibly gain access to it. The disturbance thus created 

 was evident in the bacterial examination for some weeks 

 later, and it was only on September 21 that the num- 

 ber of micro-organisms again became normal. 



It is important to notice in connection with these 

 experiments that the bacteria found belonged to the 

 well itself, and were not introduced by the accession of 

 polluting material's. The presence of the large number 

 of bacteria denotes, therefore, in such a case, disturb- 

 ance, not contamination of the well, whilst, conversely, 

 a small number of bacteria denotes prolonged quies- 

 cence of the water, and not necessarily absence of 

 contamination. 



It is therefore imperative that in the examination 

 of well-water for micro-organisms due attention should 

 be paid to the conditions recently prevailing, e.g. as to 

 whether the well has been recently pumped or dis- 

 turbed, or has beeri unused for a longer or shorter 

 period ; and unless these circumstances are duly taken 

 into consideration, the most misleading and erroneous 



