108 



Bacteria in Relation to Country Life 



tain groups of bacteria by which the organic matter 

 is rapidly destroyed without giving rise to undue offense. 

 The purified sewage is thus comparatively free from 

 putrescible substances and contains comparatively 

 few of the intestinal bacteria whose presence in drinking- 

 water is objectionable. The 

 bacteriological methods of 

 sewage -purification promise 

 to be more economical and 

 more efficient from the sani- 

 tary standpoint than the older 

 chemical methods. 



Bacteria in sewage. Sew- 



"^^^ % "-^ age may become a menace 



1 ^ - * to public health for the two- 



" 3 ^^ fold reason that it contains 



| ^k % organic substances and dis- 



^ ^ * / ease germs. The disposal of 



sewage with the least danger 

 to public safety becomes, 

 therefore, a problem of great 

 moment. By sterilizing sew- 

 age, by means of heat or anti- 

 septics, all the bacteria con- 

 tained in it can be destroyed, 

 and, by keeping it sterile, 

 its decomposition can be pre- 

 vented. The fact cannot be 

 ignored, however, that steri- 

 lized sewage, when discharged 

 into any body of water, will 



> / -*' 



Fig. 17. Sewage bacteria. 1. 

 Bacterium mes enter icus; 

 X 2,000. (Rideal.) 2. Bac- 

 terium subtilissimus; X 2,000. 

 (Rideal.) 3. Bacterium mem- 

 braneus fatulus; X 2,000. 

 (Rideal.) 4. Bacterium fusi- 

 formis; X 2,000. (Rideal.) 



5. Bacterium entiritidis sporo- 

 genes; X 2,000. (Hewlett.) 



6. Bacterium coli communis; 

 X 2,000. (Hewlett.) 7. Pro- 

 teus vulgaris; X 2,000. (Ro- 

 della.) 



