We have adverted to these nitre plantations as showing how the conditions most favourable for the development of nitrification were recognised long before anything was known as to the true nature of the process. It was only in 1877 that the formation of nitrates in the soil was proved to be due to the action of micro-organic life,[104] by the two French chemists, Schloesing and Muentz, who discovered the fact when carrying out experiments to see if the presence of humic matter was essential to the purification of sewage by soil. In these experiments sewage was made to filter slowly through a certain depth of soil (the time occupied in this filtration being eight days). It was found that nitrification of the sewage took place. By treating the soil with chloroform[105] it was found that it no longer possessed the power of inducing the nitrification of the sewage. When, however, a small portion of a nitrifying soil was added, the power was regained. From this it was naturally inferred that nitrification was effected by some kind of ferment. This conclusion was soon confirmed by subsequent experiments by Warington at Rothamsted, who showed that the power of nitrification could be communicated to media, which did not nitrify, by simply seeding them with a nitrifying substance, and that light was unfavourable to the process. Since then the question has formed the subject of a number of researches by Mr Warington at Rothamsted, as well as by Schloesing and Muentz, Munro, Deherain, P. F. Frankland, Winogradsky, Gayon and Dupetit, Kellner, Plath, Pichard, Landolt, Leone, and others. From these researches we have obtained the following information with regard to the nature of the organisms concerned in this process, and the conditions most favourable for their development. _Ferments effecting Nitrification._