254 Dr. H. Chick. The Process of Nitrification [Apr. 1, 



growing aerobically when, and only when, associated symbiotically with a 

 certain aerobic organism which removed the surrounding oxygen and created 

 an oxygen-free environment for it. Such symbioses of various grades must 

 be frequent in Nature where the " pure culture " is almost unknown. The 

 part played by the artificial pure culture in the progress of bacteriology has, 

 of course, been enormous, yet its possibilities are limited, and one must look 

 to the investigation of regulated simple symbioses for a nearer approach, in 

 the laboratory, to the workings of Nature. 



A break of two years occurred during the course of these investigations. 

 After they were again resumed, Dr. Schultz-Schultzenstein* published the 

 results of bacteriological investigations, having the same aim as the present 

 work. He isolated two kinds of nitrifying organisms from the material 

 of coke sewage filters at Karolinenhohe, near Charlottenburg, which 

 corresponded exactly to those isolated from the soil by Winogradsky, and 

 no other nitrifying organisms were found. His researches must be regarded 

 as the first published successful attempt to investigate the organisms 

 concerned with nitrification during the artificial purification of sewage, and 

 the results are entirely confirmed by the present investigation. In spite 

 of this anticipation of my identification of these bacteria, I have thought 

 it worth while to describe my isolation experiments in detail, because in a 

 subject of such technical difficulty the experience of an independent worker 

 may be of use to others. 



Section III. — Absorption of Ammonia and Ammoniacal Compounds during 



Sewage Purification. 



It has been held that a most important preliminary to nitrification, both 

 in the soil and in sewage filters, is to be found in an absorption of ammonia 

 and ammonium compounds upon the surface of the particles of soil or of 

 filtering material respectively. In the case of the soil, a long controversy 

 has taken place as to whether a physical or a chemical process was here in 

 question,! and the former view, maintained notably by LiebigJ and his school, 

 has on the whole prevailed. This "adsorption" of ammonia plays an 

 important part in the current doctrine of the action of sewage filters, which 

 considers that nitrification could not take place in the short time taken by 



* Schultz-Schultzenstein, 'Mitt. a. d. Kon.-Priifungsanst. f. Wasservers. u. Abwa's- 

 serbeseit,' 1903. 



t Way, ' Agric. Soc. England Journ.,' series 1, vols. 11—13, 1850—1852, and Mayer, 

 ' Lehrbuch der Agrikulturchemie,' 1871. Lemberg, ' Zeitschr. d. deutsch. geol. Gesellsch./ 

 vol. 28, 1876. 



% 'Liebig, 'Ann. Chem. Pharm.,' vol. 94, 1855, and vols. 105 and 106, 1858. 



