12 BACTERIA IN DAILY LIFE 



industrial importance, that doubtless before long 

 some seat of learning will do itself the honour to 

 establish one, and so set the example. 



A striking instance of the advantages of taking 

 stock, so to speak, of the attributes of bacteria 

 will occur to everyone in the revelation which has 

 followed of their powers to solve one of the most 

 knotty problems of the day the efficient manipu- 

 lation of those vast subterranean rivers of sewage 

 which honeycomb every city of the world. 



The purification which sewage underwent by 

 passing it through the pores of the soil, or, in 

 other words, by filtration, was recognised about 

 the year 1870, soon after the Rivers Pollution 

 Commissioners had begun to make their classical 

 investigations on the land treatment of sewage ; 

 but although the rapid transformation of ammonia 

 into nitrates which followed the passage of the 

 sewage through a few feet of soil was noted, yet 

 the mechanism of this nitrification process re- 

 mained a mystery until 1877, when two French 

 chemists MM. Schloesing and Muentz made 

 the then astounding discovery that this change 

 was dependent upon the vital energies of micro- 

 organisms. 



The part played by bacteria in the purification 

 of sewage thus became an established fact, and 

 the later experiments have been devoted to study- 



