192 MICRO-ORGANISMS IN WATER 



tion in the bacterial contents of water may be effected, 

 Such treatment, carefully carried out, must, therefore, 

 in the case of any water liable to dangerous contamina- 

 tion, afford the most substantial obstacle to zymotic 

 poisons reaching the consumer. 



RocJcner-Rothe' s Process. This is a somewhat similar 

 process for purifying sewage or foul waters of any kind. 1 

 It consists in collecting the sewage into an enclosed 

 well and slowly (2-9 mm. per second) pumping it up 

 into an iron cylinder. Whilst the water is slowly rising 

 in this cylinder a process of sedimentation takes place 

 in which the particles in suspension, including bacteria, 

 sink slowly to the bottom ; moreover layers of slime 

 gradually coat the inside of the cylinder, which offer 

 points of attraction and adhesion for micro-organisms 

 subsequently introduced. The purified liquid is drawn 

 off at the top of the cylinder by means of a lateral pipe. 

 The importance of this formation of slime is so far 

 recognised that in order to stimulate its production 

 chemicals, according to the nature of the water under 

 treatment, are mixed with the sewage before it is forced 

 up the cylinder. According to the bacteriological in- 

 vestigations of Wahl in Essen, Blasius in Brunswick, and 

 Kaysser in Dortmund, the results are highly satisfactory. 

 Wahl 2 records the most remarkable result that, whereas 

 in the water before treatment 1,686,000 and 5,245,000 

 micro-organisms were present in a c.c., the same water 

 on leaving the cylinder had only between 34 and 178 

 in a c.c. 



The principle of sedimentation enters also largely 

 into all the various processes of sewage purification by 

 chemical precipitation. For by far the most extensive 



1 Ccntralblatt filr Baktcriologie, vol. ii. p. 202, 1887. 



2 ' Mittheilungen iiber bacteriologische Untersnchungen Essener 

 Abwiisser,' Centra Iblatt f. allgem. Gesundheitspflege, \. 



