128 PROCEEDINGS OF THE COTTESWOLD CLUB 



water which it is usual to quote as containing so many- 

 bacteria. This small quantity of water may contain any 

 number from zero to I00,000 or more. It is said that as 

 many as 200 distinct species of bacteria have been dis- 

 tinguished in river water, but their separation and study 

 is so surrounded with difficulties that no extensive and 

 reliable classification has yet been made of them. There 

 are many points in connection with their life and death, 

 nature and growth that have yet to be made clear. It is 

 a well established fact, however, that certain species of 

 bacteria are invariably developed in certain environments 

 in preference to other species, also, that various food 

 materials are affected differently by different species, a 

 preference sometimes being given to one species which 

 upon that particular nourishing medium, or under those 

 particular circumstances entirely overgrows and puts out 

 of existence all other species. In fact every set of con- 

 ditions is conducive only to the development of those 

 organisms which belong to it, and the organisms which 

 do not belong to it are as Uttle likely to flourish when 

 accidentally introduced as a fish upon dry land. Thus 

 there are undoubtedly a number of species of bacteria 

 that are peculiar to the waters of streams and rivers and 

 which may be particularly referred to as river bacteria. 

 As rivers proceed in their course they become capable of 

 supporting other species of bacteria than those originally 

 contained in the head waters, owing to additions of salts 

 and other materials to the water, but it should be particu- 

 larly remembered that the water of a river is not rendered 

 progressively impure so far as organic material goes, but 

 varies locally to a very great extent, and to an equal extent 

 varies in regard to its bacteriology. Not only is there 

 the competition between difl^erent species of bacteria 

 which results in the survival only of the fittest, but in 

 the flowing water of a river destructive influences are at 

 work upon all bacteria and one of the strongest of these 



