BACTERIOLOGY OF SEWAGE 205 



purity alone is necessary, as at many sewage disposal 

 plants, or a higher grade of purity than this (the primary 

 standard) should be attained.' 



The Royal Commission deprecate the adoption of stan- 

 dards of bacteriological purity or of sterilisation processes, 

 both on the ground of the serious additional cost which 

 these would entail, and of the ' false sense of security ' 

 which the adoption of such measures would be apt to 

 engender. 



Some Organisms met with in Sewage. The granular 

 or sewage variety of Proteus Zenkeri is a non-liquefying, 

 non-sporing, aerobic, non-motile bacillus, and occurs in 

 the form of short and long chains and filaments. It grows 

 well in phenolated gelatin and phenolated broth, does 

 not form gas in a gelatin-shake culture, does not coagulate 

 milk, and gives no indole in broth after three days' growth. 



P. vulgaris, P. mirabilis, P. Zenkeri, are found in putre- 

 fying substances, sewage, and water. The first two are 

 motile, produce involution forms, liquefy gelatin and 

 blood-serum, and give off a decided putrefactive odour 

 from cultures. P. Zenkeri is non-motile, does not liquefy 

 gelatin or blood-serum, and the putrefactive odour is 

 absent from the cultures. All three species produce local 

 abscesses and symptoms of toxaemia when injected into 

 small animals. 



Herter and Broeck (Jour. Biol. Chem., 1911, 491) say 

 that P. vulgaris ferments dextrose and sucrose, but not 

 lactose; it destroys some native proteins, producing 

 ammonia, primary amines, hydrogen sulphide, fatty acids 

 oi high molecular weight, aromatic hydroxy-acids, indole, 

 and indole-acetic acid. They also obtained thermostable 

 toxic material from the bacteria. P. vulgaris was formerly 

 called Bacterium termo. The varieties of proteus men- 

 tioned above are now generally referred to as Bacillus 

 proteus. 



B. fluorescens liquefaciens, B. fluorescens non-lique- 

 taciens. These water organisms are short Gram-negative 

 bacilli. The former liquefies gelatin, and is motile; the 

 latter does not liquefy gelatin, and is non -motile. Gelatin 

 streaks show a fluorescent green, and the growth on 

 potatoes is brown in both cases (see p. 130). 



B. subtilis (hay bacillus] occurs in hay, air, water, 

 tseces, etc. It is about 2 // to 3 ^ long by 1 /* broad, about the 



