124 AGRICULTURAL BACTERIOLOGY. 



tamination is a matter of very serious import. Many a stream 

 which has in past years served the agricultural community for 

 one purpose or another has become useless from sewage con- 

 tamination. To meet this condition of things sanitary engi- 

 neers have been at work. They have been aided by the bac- 

 teriologist, for the most successful method of disposal of sewage 

 devised up to the present time depends wholly upon the agency 

 of bacteria. Just as we have seen them at work purifying the 

 soil, so the engineer is setting them at work purifying sewage. 

 The method adopted for purifying sewage is to destroy and 

 remove a large part of the organic matter so as to leave the 

 water comparatively pure. Various plans have been used for 

 the purpose. The use of chemicals to precipitate the organic 

 matter, which could then be removed by sedimentation, has 

 been adopted extensively. But it has proved troublesome and 

 unsatisfactory and has generally given place to a plan of treat- 

 ment depending upon the destructive powers of the decompo- 

 sition bacteria. The bacterial treatment of sewage is to-day 

 rapidly obtaining adherents among sanitary engineers and prom- 

 ises to be the method widely adopted in the near future. The 

 subject bears so closely upon our general topic that a brief 

 account of it will be here given. 



THE BACTERIAL TREATMENT OF SEWAGE. 



The bacterial treatment of sewage depends upon the destruc- 

 tive action which decomposition and putrefactive bacteria have 

 upon organic matter. Putrefactive bacteria, those growing in 

 the presence and in the absence of oxygen, have the power of 

 decomposing all kinds of organic bodies, both the nitrogenous 

 and those purely carbonaceous. Most of the solid matter in 

 the sewage is composed of these organic bodies, and it is evi- 

 dent that if the sewage can be induced to undergo a thorough 

 decomposition under the action of microorganisms, this will 

 produce a great effect upon the composition of solid matter 



