IJACTiOKI.V 



i^lH 



CorXTUY BArTEIlIA 



(\i\ P.A«Ti:iti.\ 



Wintt-r , 

 Sprini; . 

 Suinnier 

 Autumn 

 Averaije 



Bacteria of water. Streams orclinaiily coiiiain alioiit .')0(i 

 bacteria i)vv cubic centimeter, collected from tlic air and s(»il 

 over the area drained. Hie riser Seine, as it enters J*aris, lias 

 about 300 bacteria per cul)ic centimeter, 1)iit alter it receives 

 the sewage from this city it contains 2(MI,<MH) bacteria per cu- 

 bic centimeter. The su})posed self-purification of streams is 

 found to be mainl} due to dilution. Experts are impdundintr 

 I'unnincT water hi reservoirs previous to supj)l\inf^ cities, since 

 bacteria disappear from still water. Microscopic or^-anisms 

 (plankton) ui)ou which young fishes feed are found in greater 

 abundance in (luiet water, and it is thouoht that thev in turn 

 feed upon bacteria. 



AVater in ^\■ells varies great!}' in minibcr of bacteria. Arte- 

 sian wells are practically free from them : ordinarv widls mav 

 contain from 1000 to 8000 bacteria jx-r cubic centimeter. Ice 

 varies in number of bacteria accoiding to water from which it is 

 taken. ( "lear ice from the Hudson Rivei- contained .V.IS bacteria 

 per cubic centimeter, while its snow ice contained Hi S7. \\']\\ ? 



Bacteria of the soil. The nund)er of bacteria of the soil 

 varies with the amount ol moisture an<l organic debris. Sn- 

 pci-ficial layers contain from 10,000 to o. 000, ()<)() bacteria pci' 

 o'ram : if nollnte(l with orijanic del)ris, tiiev mav contain as 

 high as 100,000,000 per gram, riie innnber of bactei'ia di- 

 minishes rapidly as wt' pass down into the earth; at a dcptli 

 of from ten to fifteen feet few if any can be found. Tliis is 

 the reason that in many cities water is passed liirough sand 

 filters before it is used for driidxing pur[->oses. 



