THE BACTERIA IN NATURAL WATERS 



13 



In sea-water, too, bacterial numbers are small, as 

 noted by Russell at Naples (Russell, 1891) and Wood's 

 Hole (Russell, 1892), and in salt as in fresh water the 

 amount of bacterial life decreases in general as one 

 passes downward from the surface and outward from 

 the shore. Otto and Neumaim (1904) obtained the 

 results summarized below at various points on the 

 high seas between Portugal and Brazil. Near the 

 European coast numbers were much higher. 



BACTERIA IX THE ATLANTIC OCEAN. (OTTO AND 

 NEUMANN, 1904.) BACTERIA PER C.C. 



Nearest Land. 



Canary Islands . . . . 

 Cape \'erde Islands 



St. Paul Island 



Pemambuco 



Drew (191 2) finds high numbers of bacteria in surface 

 sea-water off the Bahamas, ranging from 13,000 to 

 16,000, falling off below 200 fathoms (in the cold bottom 

 waters at 10° C. or below) to o to 17. 



Factors Influencing the Diminution of Bacteria in 

 Surface-waters. The decrease in numbers which takes 

 place when a surface-water is stored in a pond or reservoir 

 indicates that the forces which tend to produce bacterial 

 self-purification are important ones. It is necessary 

 to consider in somewhat more detail just what these 

 forces are, in order to gauge their potency in any 

 particular instance. 



