THE BACTERIOLOGY OF SEWAGE 351 



not free access. Anaerobic organisms are always present 

 in the intestines, and after death they quickly invade the 

 whole body, and grow under very favourable conditions as 

 to temperature, the interior of the body providing in every 

 way a suitable pabulum for their growth. The aerobic 

 organisms on the surface of the dead body possibly assist 

 the putrefaction in the interior by consuming the oxygen. 

 The products of the putrefactive anaerobes are marsh-gas, 

 sulphuretted hydrogen, and free hydrogen, with traces of 

 such foul-smelling bodies as scatol, etc. 



The products of decomposition evolved by the aerobic 

 bacteria upon the surface are generally more simple in 

 character, and consist mainly of carbon dioxide and 

 ammonia. 



The Bacteriology of Sewage. — Ordinary town sewage con- 

 tains very large numbers of bacteria, often several million 

 per cubic centimetre. The number will vary greatly with 

 the freshness of the sewage, the season of the year (tem- 

 perature), and may also be affected by the addition of 

 various waste liquors from manufactories. 



We are hardly yet in a position to specify precisely by 

 name the bacteria that are constant inhabitants of sewage, 

 but the following may be regarded as the most important : 



Bacillus coli (several varie- Bacillus tholoeideum. 



ties). Bacillus cloaccefluorescens. 



Bacillus fluorescens Uque- Bacillus fluorescens stercor- 



faciens. alis. 



Bacillus fluorescens non- Proteus vulgaris. 



liquefaciens. Proteus mirabilis. 



Bacillus ramosus. Proteus cloacinus. 



Bacillus suUilis. Proteus Zenheri. 



Bacillus mycoides. Gladothrix dichotoma. 



Bacillus subflavus. Beggiatoa alba. 



