THE SEWAGE DISPOSAL PROBLEM 189 



mostly concerned in causing liquefaction of the solid material 

 contained in the sewage. 



The first stage of sewage purification has been compared to 

 gastric digestion, whereby the organic matter is split up and 

 liquefied, and just as in digestion time is an essential factor, 

 so here these anaerobic organisms must be allowed a reasonable 

 interval of time to carry out their work. 



The second stage of purification is performed by the aerobes, 

 and therefore this part of the process should be carried on in 

 an abundance of air. The organic matters having been broken 

 up, they are next converted into their ultimate products, and 

 eventually we have nothing left but a solution rich in nitrates 

 and other salts ; the gases escape into the air. These natural 

 agencies have only within recent years been scientifically applied 

 to the purification of sewage. The Royal Commission in 1901 

 issued a Report in which, referring to this method, it was said : 

 " It is practicable to produce by artificial processes alone, as 

 opposed to land treatment, from sewage or mixtures of sewage 

 and trade refuse, effluents which will not putrefy, which would 

 be classed as good according to chemical standards, and which 

 might be discharged into a stream without fear of creating a 

 nuisance." One of the great advantages of this system is that 

 there is no " sludge " difficulty. The residue is very small in 

 bulk, and hence we are saved the trouble and cost of dealing 

 with sludge. But more important even than that is the fact that 

 we get an excellent effluent in every sense of the word. 



It is worth remembering that this system of bacterial treat- 

 ment really owes its origin to the fact that Pasteur in 1862 

 showed that putrefaction is the work of micro-organisms. His 

 work was considerably advanced in this direction by Muntz, 

 Mueller, and others, who about 1872 proved that nitrification 

 also is accomplished by the agency of micro-organisms. In 1881 

 Mouras, of Vesoul, published an account of an hermetically 

 sealed, inodorous, and automatically discharging cesspool, in 

 which sewage was anaerobically broken down by "the mysterious 

 agents of fermentation." He surmised that the agents in ques- 

 tion were the " anaerobes of M. Pasteur," and it would appear 

 that this is the first record we have of the treatment of sewage 

 by allowing Nature to fulfil her functions by means of bacteria. 



The next step in the new bacterial treatment of sewage 

 came from the Massachusetts Board of Health in 1888. They 



