72 SEWAGE AND ITS PURIFICATION 



disc, and a hand lens used to assist the operation. To ehminate, 

 as far as possible, errors in counting, not only was the large 

 number of twelve plates made from each sample, but the plates 

 were divided into two batches . . . and it was found that the 

 figures obtained by the two observers, worked independently, 

 varied but a very little, and showed a close correspondence." 



The method employed for determining the liquefying 

 organisms in the Chorley experiments has not been described, 

 and presumably the counts were made from the ordinary 

 gelatine plates. Clowes and Houston, in their examination of 

 the London sewage, prepared extra " surface " plates for deter- 

 mining the liquefiers, and they remark in their report that, 

 " although this method is the best one available, it must be 

 remembered that some bacteria liquefy the gelatine so very 

 slowly that they might readily escape being counted as Hque- 

 fying germs under these conditions of experiment. This matters 

 the less since bacteriologists are in the habit of classing some, 

 at all events, of these bacteria as non-liquefiers." 



The following is a list of some of the sewage bacteria which 

 have been found by various observers : 



BACTERIA OCCURRING IN SEWAGE. 



Note. — L, Liquefying gelatine ; NL, not liquefying ; SL, slightly 



liquefying. 



Obligatory Anaerobes. 



Bacillus amylobactev, L (Clostridium hutyvicum). 



B. entevitidis spovo genes, L ; cadaveris spore genes, L ; butyricus, L. 



Give much gas. 

 Spirillum rugula, L. Very active ; gives rise to faecal odour. 

 S. amyliferum. Acts as a vigorous ferment. 



Facultative Anaerobes or Aerobes. 



B . fluorescens liquefaciens, L, and non-liquefaciens, NL ; megaterium, L ; 



magnusj spinosus, liquefaciens, L ; mesentericus, L. Several 



varieties in London sewage produce HgS. 

 B. vermicularis, L ; liquidus, L ; ramosus, L ; mycoides, L ; fuscus, NL ; 



nubilus, L; cloaca, L; ubiquitus, NL; reticularis, SL ; cereus, L; 



circulans, L ; hyalinus, L. All reducing nitrates to nitrites 



and NH3. 

 B. aquatilis, SL (grows luxuriantly in ammonia solutions) ; brunneus, 



NL; helvolus, L; and superjicialis, SL. Not reducing nitrates. 

 B. saprogenes, I., II., III. ; pyogenes and copro genes fetidus. 

 B. putrificus coli, NL ; fluorescens putridus, L. Decompose albuminous 



substances, liberating NH3. 

 B. coli communis, NL ; acidi lactici, NL ; lactis aerogenes, NL. All 



producing gas. 



