124 BACTERIOLOGY 



Variations in water depending on source,— The bacteria 

 which hve in water multiply considerably when it has been 

 stagnant for some time, and observations made in flooded 

 districts show that the bacilli of anthrax, tyiilioid fever, and 

 cholera are capable of growth on dead portions of plants 

 when moist. Koch has also fomid the bacillus of mouse 

 septicemia in water, and the Staphylococcus pyogenes aureus 

 is not seldom encountered. This is explained by the fact 

 that fresh water contains carbon dioxide ; and, moreover, 

 large numbers of germs are often found also in artificial 

 aerated waters, such as seltzer, which contain the gas. 



In fresh spring-water the germs are said to sink to the 

 bottom, and hence in some wells which have been disused 

 for a considerable time a larger proportion of germs is 

 demonstrable after the first pumping than later. The 

 micro-organisms are not, as a rule, carried to the well by the 

 ground water, but come from the surface and the superficial 

 layers of soil, and the more ground-water is caused to flow 

 in by constant pumping, the fewer will become the bacteria 

 contained in the water of the spring. When, however, the 

 distance of the spring from the surface is small, or when 

 the well has been made artificially by damming up the 

 earth, or when sewers extend down into the ground-water, 

 then this water in which the spring stands will be very rich 

 in bacteria (Arnold). 



A drinking-water which can be termed good from a bac- 

 teriological point of view must be poor in fission-fungi, and 

 consequently must not have stagnated in the water-pipes, 

 and there must be security that no communication can take 

 place by crevices and fissures between the reservoir or the 

 mains on the one hand, and drains or sinks on the other. 

 According to Etibner, the natural filtration through the 

 soil under which the spring water lies purifies it so 

 thoroughly that it comes to the light of day in an almost 



