i 9 4 SCIENCE PROGRESS 



suspended matter before attempting to purify it on land or 

 by filters. This is done by screens and detritus tanks or sedi- 

 mentation tanks of various designs. 



Animal Life in Bacterial Filters 



Dr. Barwise has recently drawn attention to the fact that 

 bacterial beds are not correctly so called. He contends that 

 they are, in the words of Sir James Crichton Browne, much 

 more like " entomological menageries." He has not attempted 

 to classify the inhabitants found there, but believes that in small- 

 grain filters, at any rate, the destruction of organic matter is 

 mainly effected by small river worms, and of these there are 

 something like a thousand species. Amongst others, he has 

 recognised Naididce, TubificidtT, and Polychcetce, etc., in enormous 

 numbers. Then, again, in the large-grain filters there are large 

 worms, leeches, and countless numbers of larvae of gnats and 

 flies. In addition to the above, there are water Crustacea — e.g. 

 Cyclops, Cyprides, freshwater shrimps, centipedes, water-spiders, 

 etc., etc. There is at present very little information available 

 as to the life history, food habits, and the various parts which 

 these various animals play in connection with sewage purifica- 

 tion ; but it is obvious that, their presence having been proved, 

 their function opens up a most interesting field of study to the 

 zoologist, and a clear determination on this point may prove 

 of vast importance in the extremely difficult and many-sided 

 problem of sewage disposal. 



The Travis Hydrolytic System of Sewage Tanks 



This system of sewage treatment has been introduced by 

 Dr. Owen Travis, and is to be seen in actual use at Hampton 

 (Middlesex) and Norwich. The main object is the separation 

 of the suspended solids and colloidal matters from the sewage 

 before it reaches the filtration area or is discharged into the 

 sea or tidal river. The " Hampton Doctrine," as it is called, 

 insists that the purification of sewage is primarily and essentially 

 physical, and only incidentally and consecutively vital — that is 

 to say, that the physical separation of the impurities from the 

 sewage constitutes the all-important part of the purification 

 process, and that the bacterial and other life operations are 

 subservient to this initial effect. It will be seen from this 



