a class comprising: a) phagocytes which consume living bacteria; 

 &) large , organisms inimical in other ways to bacteria. The action 

 of the saprophytes tends to increase the fertility of the soil; they 

 produce ammonia, fix nitrogen and so on. 



Some of them cause a liberation of nitrogen during the decom- 

 position of organic matter and are to this extent injurious. This 

 action, however, is either much restricted or is counterbalanced by 

 fixation processes. 



On the other hand, the phagocytes and similar organisms are 

 detrimental to fertility, because they limit the number of bacteria 

 and therefore the rate at which ammonia is produced. 



Between those two classes of organisms there is an equilibrium 

 under natural conditions and the amount of decomposition is much 

 less than might be expected from the quantity of organic matter 

 present. 



When toluene is added or when the soil is heated to 98 C. 

 the phagocytes are killed but not the bacterial spores, which germi- 

 nate when toluene is removed and the soil again moistened, and 

 the resulting organisms multiply with great rapidity since they are 

 now freed from the attacks of their enemies and the competition 

 of larger organisms. 



The removal of nitrifying organisms seems to have little effect 

 on the growth of plants. 



A. D. HALL. The Conservation of the Fertility of the Soil. 



The Journal of the Board of Agrictdture. Vol. XVII, n. 2. London, 

 May 1910, p. 114. 



" In considering the value of various systems of farming it be- 

 comes a matter of prime importance to get some idea of how far 

 the fertility of the land is being preserved, and whether the succeed- 

 ing generation of farmers is likely to find the cropping power of 

 the soil improved or deteriorated by the treatment it has received. 

 It is pretty, clear that in many parts of the world the natural riches 

 contained in the virgin soils are being rapidly depleted; this may 

 be deduced from the constant westward movement of certain classes 

 of farmers in the United States and Canada, though in some parts 

 of America the soil seems to be able to yield good crops for an 

 indefinite period. On the other hand, many European soils have 

 reached a sort of constant level of production, and get neither 

 richer nor poorer, although they have been in cultivation for many 



