Warington Smyth, Notes of a Journey on the Upper Mekong (1895); Five Years in Siam (1898); Harmand, Le Laos et les populations sauvages de l'Indo-Chine (1880).
Warington states that the proportion of nitrogenous to non-nitrogenous matter in the digestible part of potatoes is as i to io 6.
Mintz and others had proved that nitrification was promoted by some organism, when Winogradsky hit on the happy idea of isolating the organism by using gelatinous silica, and so avoiding the difficulties which Warington had shown to exist with the organism in presence of organic nitrogen, owing to its refusal to nitrify on gelatine or other nitrogenous media.
In addition to the bacterial actions which result in the oxidization of ammonia to nitrous acid, and of the latter to nitric acid, the reversal of such processes is also brought about by numerous bacteria in the soil, rivers, &c. Warington showed some time ago that many species are able to reduce nitrates to nitrites, and such reduction is now known to occur very widely in nature.
Fermentation, &c.: Warington, The Chemical Action of some Micro-organisms (London, 1888); Winogradsky, " Recherches sur les organismes de la nitrification," Ann.