Bacterial Treatment of Sewage. 385 



index of the decrease of the putrescent matter, and therefore of the 

 efficiency of the filtration. Also the amount of nitric nitrogen in the 

 filtered effluent indicates the extent of conversion of putrefactive nitro- 

 genous matter in the tank effluent into non -putrefactive nitrogenous 

 compounds, so that the higher this figure is the more active, as a 

 general rule, is the purifying power of the filter. 



The question of sewage disposal is a highly technical one, and 

 only those who have had practical experience can imagine the diffi- 

 culties which have to be overcome, and therefore Local Authorities 

 and others who have this matter to deal with should be careful before 

 committing themselves, unless advised by experienced engineers, as 

 a method of disposal which may answer in one case may prove useless 

 in another. It is important to remember that it is a chemical and 

 bacteriological, as well as an engineering question, and the chemical 

 composition of the sewage, which I have previously mentioned, varies 

 greatly, and has to be taken into consideration in forming an opinion 

 as to the method which is likely to prove most satisfactory. 



In conclusion, I wish to say that the evidence given before the 

 Royal Commission of Sewage Disposal has been of the greatest value 

 to the Sanitary Engineer, but until the Commissioners' final report 

 is published we are not in a position to say which of the bacterio- 

 logical methods at present recommended is the best ; and no doubt, 

 as I mentioned above, this to a large extent is governed by the cir- 

 cumstances in each case; neither can it be said that we have arrived 

 at finality in our knowledge as to the best means of availing ourselves 

 of Nature's processes, but that we are on the right lines is perfectly 

 certain. 



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