28 WILLIAM M. HAMLET. 



of the suspended matter and even the partial destruction of 

 putrescible matters by microbial agencies afforded sufficient ground 

 for justifying the process, at all events as a preliminary measure. 

 Whether this preliminary treatment is to be supplemented by 

 further treatment, either by passing through coke-beds or by land 

 irrigation, or by any other method, is a matter largely dependent 

 on circumstances. In the present case there are practical points 

 which first of all demand consideration, and although it may 

 be most desirable to obtain an effluent chemically pure and 

 bacteriologically above suspicion of danger, it is to be thought of 

 that an effluent not altogether satisfactory in one or other, or 

 even in both, of these respects may yet fulfil all necessary 

 requirements without passing out of the range of practicability. 

 In certain cases it may be imperative to obtain an effluent 

 bacteriologically sound, but it does not follow that a similar result 

 is urgently called for in other cases, as, for example, where an 

 effluent is turned into a watercourse which is not used for drinking 

 purposes, and which already may contain practically all the 

 bacteria that are found in sewage." 



The history of fermentation, putrefaction, and nitrification has 

 latterly been so frequently repeated that I hesitate in doing much 

 more than mention dates, general results, and the names of those 

 whose researches have opened up for us the possibilities of sewage 

 zymolysis. The earliest observer to perceive the low forms of life 

 that play so important a part in the decomposition of animal matter, 

 was Leewenhoeck, 1 who in 1675 was not a little astonished in 

 getting glimpses of that nether world — invisible to the unassisted 

 eye — that world of life we now recognise as bacteriology. I can 

 only mention men's names as the 'stepping stones to higher things' 2 

 in linking this seventeenth century science worker with the latest 

 developments of this subject. 



1 Leewenhoeck — Opera omnia, 1722. 



2 Leewenhoeck 1675, Muller 1773, The Abbe Spallanzani 1777, Schulze 

 1836, Ehrenberg 1838, Schwann 1839, Dujardin 1841, Helmoltz 1843, 

 Cohn 1853, Schroder and Von Dusch 1854, Davaine 1859, Pasteur 1862, 

 Van Tieghem 1864, Schloesing and Miintz 1877, Beyerinck 1888, Wino- 

 gradsky 1890, Warrington 1891, Omeliansky 1900. 



