320 Professor Frank Clowes [March 9, 



Fewage contains many different species of bacteria, some of which 

 have been described and figured by Dr. Houston.* As is seen in 

 Figs. 2, 3, 4, some of these bacteria possess motile tail-like flagella, 

 and by the movement of these the minute organisms maintain a 

 rapid progress through the liquid. Bacteria which are devoid of 

 flagella and which cannot traverse free paths in the liquid are shown 

 in Figs. 5, 6, 7, 8. In Fig. 6 the spores of these minute vegetable 

 organisms are seen interspersed among the organisms themselves. 

 The organisms have two methods of multiplying, by fission and by 

 producing spores ; the spores have the power of retaining vitality 

 under conditions which are fatal to the organisms themselves. It is 

 found that none of these are selectively retained by a coarse coke-bed 

 during the treatment, but that all the species make their appearance in 

 only slightly diminished numbers in the purified effluent from the 

 coke-bed. The average reduction in the number of the baeteria in the 

 6ewage by one treatment in a coarse coke-bed amounted to only 27*7 

 per cent. It would therefore appear that the different species of 

 bacteria assist one another in the purifying action, and by producing 

 either contemporaneous or consecutive effects upon the sewage secure 

 its purification : in bacteriological language, their action is either 

 symbiotic or metabiotic, or possibly of both kinds. The organisms 

 b em to establish and maintain a condition of equilibrium amongst 

 themselves in the coke-bed, since attempts to artificially increase the 

 number of certain species have thus far failed. 



It appears that in the above processes there is no separation of the 

 bacterial action which takes place in the presence of air from that 

 which occurs only in the absence of air, and both processes probably 

 proceed side by side in the open coke-bed. The anaerobic, or so- 

 called " septic " treatment, during which cellulose is slowly resolved 

 with separation of hydrogen and methane, is, however, sometimes 

 made to precede the more truly aerobic treatment. 



One result of the anaerobic treatment is the liberation of large 

 volumes of combustible gas, and this gas has been employed at some 

 works for illuminating purposes on the incandescent principle. 



The general products from both processes of bacterial action are 

 carbon dioxide, water, ammonia, nitrogen, hydrogen and methane ; 

 and in the aerobic changes the ammonia is subsequently oxidised into 

 nitrite and nitrate. 



The experience obtained from several years' experimental 

 bacterial treatment of the sewage from several of our largest cities 

 has recently been published. 



In 1893 the London County Council constructed an acre coke- 

 bed about three feet in depth at the Barking Outfall of the North 



* The illustrative figures in this article have been selected from Reports on 

 ' The Bacteriology of London Crude Sewage ' and on ' The Bacterial Treatment 

 of Crude Sewage.' by Dr. Clowes and Dr. Houston, issued by the London County 

 Council (F. S. King and Son), and were originally produced from microphoto- 

 <rraphs taken by Dr. Norman from Dr. Houston's cultivations. 



