356 APPLIED BACTERIOLOGY 



showing that true purification has begun, and that there is 

 a store of oxygen that could be drawn on, as a guarantee 

 against possible putrefaction. 



It is impossible to judge of the quality of an ejffluerd by 

 any bacteriological Tueans at present at our disposal, but 

 various chemical standards have been proposed. 



In a report on the septic tank process (Exeter) we have 

 suggested such a chemical standard, laying stress on the 

 necessity for insisting on the presence of nitrates in 

 appreciable quantities. 



It is at least safe to prophesy that in the near future all 

 sewage works which do not discharge direct into the sea 

 will be required to provide themselves with bacterial filters, 

 and to produce an effluent conforming to some kind of 

 standard. 



