224 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



and comparatively small quantities of carbon dioxide. H 

 confirms the conclusions of previous observers, by showin) 

 tbat in solutions of organic matter the nitrous organism 

 thrive, while the nitric organisms lose their vitality. Hi 

 also finds that the nitrous organism cannot carry oxidatioi 

 beyond the stage of nitrite, whereas the nitric organism onlj 

 oxidises nitrites to nitrates. He adds the further importan! 

 conclusion, that the presence of peaty or humus mattei 

 appears to preserve the vitality of the nitric organisms 

 during the earlier stages of the fermentation process, and 

 establishes conditions whereby it is possible for the nitric 

 organisms to thrive simultaneously with the nitrous. This 

 latter conclusion has an important bearing on the oxidation 

 of organic matter in nature, and especially under the controlled 

 conditions which obtain in modern processes for the biological 

 purification of sewage. 



In all the researches on the nitrifying organisms referred 

 to in the foregoing pages, the conditions have been essentially 

 laboratory conditions, where the solutions of organic mattei 

 have been exposed to air, so to speak, in bulk, either by 

 simple exposure of a solution in a flask, by shaking with air, 

 or by bubbling air through ; the element of surface action 

 has not been brought into play. It is clear on reflection that 

 if the solution to be nitrified could be passed in a thin film 

 over a large surface, with free circulation of air, the conditions 

 for oxidation would be very much more favourable ; for not 

 only would the presence of ample oxygen be assured, but also 

 the extended surface would afford a substratum for a greatly 

 increased development of the necessary organisms. It is the 

 application of these principles which has led to the modern 

 developments in sewage purification processes. 



In 1869 Sir Edward Frankland, acting on behalf of the 

 Royal Commission on Sewage Disposal then sitting, made his 

 classical experiments on the so-called intermittent filtration 

 of sewage through soil. He made use of cylinders fifteen feet 



