18 
president’s address. 
ferment theory of nitrification could be further strengthened. 
Although, however, the greater part of this evidence has been 
before the scientific public for more than seven years, the theory 
that nitrification is due to an organism can hardly be said to have 
obtained any general acceptance ; it has not, indeed, been seriously 
controverted, but neither has it been embraced. It is surely 
incumbent on those who discuss sanitary and agricultural questions 
either to accept the theory, and henceforth regard the oxidation of 
nitrogenous organic matter as effected solely by living organisms, 
and confined to the conditions suitable for their activity, or to 
adduce some evidence that nitrification may take place in soils and 
Avaters by simple contact Avith oxygen, Avhen all organisms have 
been absolutely excluded. Schlusiug has apparently given a final 
bloAV to the theory that air exists in a condensed state in the pores 
of a soil, and may on that account exert special oxidizing poAvers, 
by his recent experiments (Ann. de la Science Agronomique, 1 884, 1 ), 
shoAving that the gases in a vegetable soil simply occupy the normal 
volume due to temperature and atmospheric pressure.” 
I Avill noAV come to the practical bearings of this subject xipon 
soils and upon agriculture. It is abundantly evident that, the 
special organism Avhich nitrifies ammonia exists in the surface soil 
of all fertile land, and Mr. Warington has elucidated the fact, that 
it is only in the surface soil that such an organism occurs. It Avas 
found that the nearer the soil Avas taken from the surface, the more 
rapid its nitrifying effects ; and Avhen samples Avere taken at a 
greater depth than nine inches, there Avas cither no action Avhatever, 
or only a very feeble one, Avhich took a long time to inciibatc. 
The distribution of Bacteria in soil has been microscopicalh' 
investigated by Koch, and he states that the micro-organisms 
in the soils he has examined diminish rapidly Avith increasing 
depth, and at the depth of three feet the soil is nearly free from 
Bacteria. 
Mr. Warington says: “Some important practical conclusions 
seem to follow from the limitation of the nitrifying organism 
to the upper soil. Thus it is evident that the oxidation of 
