Makgill.— Nature's Efforts at Sanitation. 14? 



purifier by means of drain-pipes and leave it unchanged on 

 our sea-beaches or in our streams to putrefy and pollute the 

 neighbourhood. 



How Towns should be dealt with. 



In towns the pipes have to be used, however, and it is 

 at the outfall of the sewers that we should provide systems 

 of treatment which, in a measure, follow Nature's methods, 

 and utilise, or at least render innocuous, the accumulated 

 filth. There is a necessity in all such systems for keep- 

 ing separate the sewage proper — that is, the waste from 

 domestic and trade processes — from the storm-waters and 

 natural streams. If we let them mix we have too large a 

 volume of fluid to deal with, while at the same time the 

 sewage is not sufficiently diluted to prevent its becoming 

 dangerous and offensive. Unpolluted storm-water can be 

 readily disposed of, while the sewage proper, being moderate 

 in amount, can be submitted to any of the treatment pro- 

 cesses which now form an essential part of all modern drain- 

 age schemes. Chief among such processes are the sewage 

 farm, the chemical treatment, and the septic tank, or biological 

 system. 



It must be admitted with regret, as the Royal Commission 

 on River Pollution long ago pointed out, that the sewage of 

 towns must be treated as a nuisance to be got rid of in the 

 cheapest and most efficient w r ay, but must not be regarded as 

 a source of profit. We cannot copy Nature's perfect economy 

 when we break her rules to the extent of huddling together in 

 large communities. 



The sewage farm, to be a success, requires a large area of 

 ground and a soil specially adapted as regards its porosity, and 

 so on, and, though it is closely allied to natural principles, we 

 have a difficulty in preventing our humus from being drowned 

 unless a very large area of land be available. Thus it has been 

 calculated that London's sewage would require a farm of 100 

 square miles. The chemical process is costly, and at best 

 does not produce a very good effluent, while a difficulty re- 

 mains in the disposal of the sludge, the precipitated organic 

 matters. In the septic tank, however, every advantage is 

 taken of the forces of Nature, the principle being to utilise 

 the two great bacterial actions — first, the solution of organic 

 matters, which we have seen in the decomposing body ; and, 

 second, the nitrification of the dissolved products, which we 

 know takes place in the earth. The result is an effluent 

 of clear fluid without smell or offence, a mere solution of 

 nitrates and other simple salts. 



Many forms of apparatus have been constructed which 

 work on this principle, all nearly equal in efficiency. Advan- 



