398 CLINICAL BACTERIOLOGY. 



for cultivating these bacteria from water has been consid- 

 ered in the discussion of typhoid fever (p. 178) and of cholera 

 (p. 195). At this point it may be briefly repeated that by 

 the addition of one per cent, peptone and y 2 per cent, 

 sodium chlorid, the water to be examined itself constitutes 

 a nutrient medium, so that in this way large quan- 

 tities of the fluid can be employed, whereas in earlier 

 investigations a fraction of a drop had to suffice, and, as a 

 result, the pathogenic germs were readily overlooked. 



The saprophytic water-bacteria multiply in water to an 

 unlimited degree. For the pathogenic bacteria, however, 

 while the possibility of preservation often exists, but rarely 

 is opportunity for proliferation in water afforded. To this 

 end there are necessary a favorable external temperature 

 (summer) and, further, solid particles of vegetable or ani- 

 mal origin, to which the bacteria adhere, which serve as 

 nutrient medium, and which, at the same time, afford the 

 bacteria protection from the competition of saprophytes. 

 The exciting agents of typhoid fever and of cholera appear 

 to survive in ordinary water for days, and even for weeks. 

 Some observers even believe that cholera-vibrios may at 

 first undergo multiplication in water. As a rule, however, 

 the pathogenic germs are suppressed sooner or later in 

 water in consequence of overgrowth by the saprophytes. 



Self-purification of Water. The microorganisms pres- 

 ent in water are derived from the surface of the earth, the 

 air, from waste water and the sewage of cities, emptying 

 into the water-courses, from cesspools communicating with 

 imperfectly constructed subsoil-wells, etc. The pollution of 

 streams by cities is a most prominent factor ; the Seine at 

 Ivry, for instance, contains 32,500 germs to the cubic cen- 

 timeter ; below Paris, in Asnieres, the number is 12,800,000. 

 Fortunately, if renewed contamination does not take place, 

 streams purify themselves (Pettenkofer). The microor- 

 ganisms settle and are carried to the bottom, partly with 

 the constituents suspended in the water and with the in- 

 soluble earthy combinations that form from calcium and 

 magnesium bicarbonates after escape of the carbon dioxid. 

 Light also in a high degree exerts an injurious influence 

 upon the microorganisms present in water down to a 

 depth of about two meters. The organic substances con- 

 tained in water are gradually consumed by bacteria and 

 algae. 



