Nitrification with reference to the Purification of Sewage. 241 



in favour of a view that the Todas are a people who have once had a culture 

 higher than that they now possess. When the customs and institutions of 

 the Todas are compared with those of other parts of India, it is found that 

 there is most resemblance with the people of Malabar; and the view is 

 advanced that the Todas migrated to the Nilgiri Hills from Malabar, and are 

 possibly allied in race to the two chief castes at present existing in that 

 district, the Nairs and Nambutiris. 



In addition to the work on the Todas, observations were also made on 

 members of other tribes. The vision of the Sholagas and Uralis, two wild 

 jungle tribes, was investigated* from several points of view ; and observa- 

 tions, chiefly on colour-blindness, were made on members of other castes or 

 tribes. 



A Study of the Process of Nitrification with reference to the 

 Purification of Sewage. 

 By Haeriette Chick, D.Sc. 



(Communicated by Professor H. Marshall Ward, F.R.S. Received April 1. — Read 



May 11, 1905.) 



Introduction. — That nitrification is a biological process was first established 

 with certainty, after long controversy, in 1888, by the decisive experiments of 

 Plathf and Landolt,i who in this matter confirmed the previous researches 

 of Schlosing and Muntz,§ Warington|| and Soyka.lF 



The discovery of the active living agents followed soon after, when 

 Winogradsky** (1890 to 1892) isolated the two sets of organisms which, as 

 he showed, co-operate to produce natural nitrification. These were (1) the 

 nitrite-producer, B. nitrosomonas, which oxidises ammonia to the nitrite stage 

 only, and (2) the nitrite-producer, B. nitrobacter, which carries on the 



* ' Bull. Madi as Government Museum, 1 1903, vol. 5, p. 3. 



t Plath, 'Landw. Jahrbucher,' v. H. Thiel, vol. 16, lift. 6, and 'Oentralb]. f. Agri- 

 kulturchem. v. Biedeiniann, 1 vol. 17, 1888. 



1 Landolt, ' Deutscli. Landw. Presse,' vol. 15, and ' Ceutralbl. f. Agrikulturchem., 7 vol. 

 17, 1888. 



§ Schlosing and Muntz, ' Comptes Rendus, 1 vols. 84 and 85, 1877, and vol. 89, 1879. 

 || "Warington, 'Journ. Chem. Soc.,' vol. 33, 1878, and 'Landw. Versuchsst.,' vol. 24, 

 1880. 



H Soyka, ' Zeitschr. f. Biologie/ vol. 14, 1878. 



** Winogradsky, 'Ann. de PInst. Past.,' vol. 4, 1^90, and vol. 5, 1891 : also 'Archives 

 des Sci. bioL de St. Petersb.,' vol. 1. 1892. 



