58 K. GREIG-SMITH. 



the points of the soil particles, and although the vapours 

 of the disinfectants may not transport the agricere, the 

 condensed vapour on the surfaces of the particles will cause 

 a segregation. Instead of uniformly coating the particles, 

 the agricere is deposited on the raised angles of the soil 

 fragments. The agricere is the remainder of the ether- 

 soluble material of the organic matter of the soil, and as 

 such must be concentrated in the decomposing organic 

 matter, saturating it, as it were, and hindering its rapid 

 decomposition by bacteria. With its removal, the organic 

 matter should be more easily decomposed and the fertility 

 increased. There is the probability that it is the agricere 

 which prevents the too rapid decomposition of the organic 

 matter of sandy soils, that it prevents the soil from becom- 

 ing a raw sand. 



My experiments with organic matter artificially covered 

 with paraffin, did not show the benefit expected from an 

 ether or chloroform treatment, but that was undoubtedly 

 caused by the dried blood or casein, used for the purpose, 

 swelling upon being moistened, and so breaking the paraffin 

 covering. 1 The direct influence of the agricere is therefore 

 difficult to prove, and so it may be taken that its segrega- 

 tion, caused by the volatile disinfectants, plays a certain 

 though perhaps a small part in the increased fertility. 



The Possible Nature of the Limiting Factor. 

 Among the various possibilities which may ultimately 

 explain the nature of the factor that limits the increase of 

 the bacteria in soil, we cannot imagine that it is a physical 

 condition, for such a state could not propagate itself. A 

 colloidal condition of the humus or the clay, if destroyed 

 by disinfectants or by air-drying, could not be restored by 

 the addition of 5% of untreated soil as Russell and Hutch- 

 inson has shown. These authors say that it must be 



1 Proc. Linn. Soc. New South Wales, 1913, 740. 



