lxxxviii. ABSTRACT OF PROCEEDINGS. 



determined by exhaustion of all suitable pabulum, thus, in 

 part at least, accounting for the gradual decrease to which 

 reference has been made. 



If these experimental results be applied to the consider- 

 ation of natural waters it is evident that very much the 

 same selective process must take place. At first the 

 bacteria washed in may continue to live upon the particular 

 organic matter washed in with them, but as this becomes 

 diluted and destroyed by natural processes occurring in the 

 river, species after species will be deprived of the necessary 

 nourishment and so will speedily or slowly die of starvation. 

 The ultimate bacterial flora of the water will obviously be 

 composed of those species which regularly lead a free 

 existence in nature, and whose nutritive requirements are 

 satisfied by the simple materials permissible in food potable 

 water. The importance of these considerations lies in the 

 fact that given sufficient time even polluted streams would 

 undergo self purification. 



The author then proceeded to describe the manner in 

 which these particular germs were bred, the mode of their 

 occurrence, the way in which they are dispersed and 

 eventually carried into the water courses. He instanced 

 two typical cases, that of an outbreak of typhoid fever at 

 Camborne in Cornwall and at Lansen in Switzerland. In 

 neither of these cases was the polluting material originally 

 great in amount: the extensive effects must be ascribed to 

 multiplication of the bacilli after their entry into the water. 

 How far typhoid bacilli can be carried by a river is appar- 

 ently not determined by available data, but it is neither 

 judicious nor practicable to set any limit of safety in this 

 matter. 



The author referred to the different modes adopted for 

 the purification of water, making special reference to puri- 

 fication by subsidence and the effect of light upon bacteria 



