no SEWAGE AND ITS PURIFICATION 



Any amides of the acids are hydrolysed, with liberation of 

 ammonia. 



Hoyer^ has shown that acetic acid bacteria can Hve in 

 absence of air, and then reduce colouring matters such as 

 indigotin, methylene blue, and litmus, with liberation of CO2. 

 They can obtain their nitrogen from peptone, asparagin, 

 nitrites, and ammonium salts, and their carbon from acetates, 

 lactates, and sugar. This shows that aerobic and anaerobic 

 species are by no means rigidly separated; very few are 

 obligatory in either sense. 



Fungi and most vegetables secrete ferments, called by 

 Bertrand '* oxydases," which are capable of acting on phenol 

 and the aromatic compounds in the second stage. W. H. 

 Perkin states that pyridine, benzene, and naphthalene deriva- 

 tives disappear in the contact beds at Manchester. 



Rapid oxidation of organic acids in presence of traces of 

 ferrous salts, which always exist in sewage, seems to take place 

 without the agency of bacteria.^ 



5. Solution of Cellulose and Fibrous Matters. — Mitscherlich in 

 1850 proved that cellulose was dissolved by fermentation ; and 

 Van Tieghem,^ in 1870, describes the most active organism as 

 B. amylohacter, anaerobic, and derived principally from the 

 intestines of animals. It is always found in putrefying infu- 

 sions, and hydrolyses sugars and starch as well as cellulose, 

 yielding butyric acid and hydrogen, whence its later name of 

 B. butyricus. Tappeiner^ fermented cotton- wool and paper 

 pulp in a weak nitrogenous solution, and obtained CO2 and 

 methane in neutral, and CO2 and H in alkaline solution. 

 Hoppe-Seyler^ in 1886, finding only traces of residue, con- 

 cluded that at first a soluble carbohydrate was formed by the 

 action of water, and then split up into CO^ and CH4 : 



C,H,A = 3C02 + 3CH,. 



If more water took part, less CH4 and more H would be 

 obtained. Horace Brown ^ found that a cellulose-dissolving 

 enzyme in the digestive tract of herbivora was secreted by the 

 food plants themselves, and came into activity under favour- 



1 Chem. Ceiitralblatt, 1899, i., 854. 



2 Fenton and Jones, Chemical Society's Transactions, January, 1900, 69. 

 2 Zeit. Phys. Chem., vi., 287, and De Bary's Lectures. 



^ Zeits.f. Biol., xxiv., 105. ^ Zeits.f. Biol., x., 401. 



6 Jonrnal of the Chemical Society, 1892, Ixi., 352. 



