ANNIVERSABY ADDRESS. 17 



An examination of the soil from any part of the earth's surface 

 discloses the presence of organisms, in the form of cocci, bacteria, 

 and bacilli, which have the common property of converting the 

 nitrogenous constituents common to all dead organic matter into 

 harmless bodies, such as nitrites and nitrates of whatever base 

 may be present, and so are removed, dissolved in water, and 

 perhaps taken up by the roots of plants, the materials, the 

 decomposition of which is otherwise offensive to the senses and 

 injurious to the health of the living. Moreover, these organisms 

 are mainly in the uppermost layers of the soil, diminishing in 

 number downwards, so that at a depth of five or six feet there 

 are comparatively few — this is why it is mainly in the surface 

 layers that, on the one hand, the greatest amount of decomposition 

 of organic matter takes place, and, on the other, the rootlets of 

 plants are mainly found, for it is now clear that plants are largely 

 dependent upon these nitrifying organisms for their food. This 

 is proved inferentially by the fact that these organisms are distri- 

 buted everywhere co-extensively with plants, and directly by the 

 fact that if fertile soil be heated to a temperature sufficient to 

 destroy the vitality of the organisms, that soil is no longer fertile, 

 it has become sterile, plants will not grow in it, and it will no 

 longer purify sewage as it did before. The term " living earth " 

 has been most happily applied to the natural soil, and a curious 

 experiment is to chloroform such soil and see, that when the 

 activity of its living organisms is thus suspended, it is powerless 

 to decompose organic matter, in short, to dispose of sewage matters 

 as it did before. If now the chloroform is allowed to evaporate, 

 the active properties of the soil as regards purifying sewage return. 



The discovery of these nitrifying organisms and our know- 

 ledge of their conditions of activity, have given us much more 

 definite notions of what goes on in sewage farms, and to my mind 

 point to such farms, where the proper soil in sufficient area, in a 

 convenient locality, and at a reasonable price can be had, as at 

 once the most natural and most efficient mode of disposing of 

 sewage. At the Botany Farm, according to the latest figures, each 



B— May 2, 1894. 



