I30 



NA TURE 



[June 7, 1900 



bacteria possess motile tail-like flagella, and by the move- 

 ment of these the minute organisms maintain a rapid 

 progress through the liquid. Bacteria which are devoid 

 of flagella, and cannot traverse free paths in the liquid, are 

 shown in Figs. 5, 6, 7 and 8. In Fig. 9, the spores of 

 these minute vegetable organisms are seen interspersed 

 amongst the organisms themselves. The organisms have 



Fig. 2. — "Sewage proteus." Micrcscopic preparation stained by V. 

 Ermengem's method, showing one flagellum at the end of each rod ; 

 from a 24 hours' growth agar culture at 20° C. X 1000. 



two methods of multiplying, by fission and by producing 

 spores : the spores have great power of retaining vitality. 

 It is found that none of these bacteria are selectively 

 retained by a coarse coke-bed during the treatment, but 

 that all the species make their appearance in but slightly 

 diminished numbers in the purified effluent from the 

 coke-bed. The average reduction in number of bacteria 



Fig. 3. — B. mesentericus. Sew.ige variety )■".. Microscopic preparation 

 stained by V. Ermengem's method, showing numerous flagella, from a 

 20 hoturs' agar culture at 20° C. X 1000. 



suffered by the sewage by one treatment in a coarse 

 coke-bed amounted to only 277 per cent. It would 

 therefore appear that the different species of bacteria 

 assist one another in the purifying action, and by pro- 

 ducing either contemporaneous or consecutive effects 

 upon the sewage secure its purification : in bacterio- 

 logical language, their action is either symbiotic or 



NO. 1597, VOL. 62] 



metabiotic, or possibly of both kinds. The organisms 

 seem 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 



Fig. 4.— j5. vtesentericus. Sewage variety I. Microscopic preparation 

 stained by V. Ermengem's method, showing numerous flagella ; from 

 a 20 hours' agar culture at 20° C. X 1000. 



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. 



