238 



CONTRIBUTIONS TO OUR KNOWLEDGE OF .SOIL- 

 FERTILITY. 



x.The Action of Fat-Solvents upon Seivage-sick Soils. 



By R. Greig-Smith, D.Sc, Macleay Bacteriologist to the 



Society. 



In a paper upon sewage-sickness in soil and its amelioration by 

 partial sterilisation, Russell and Golding* discuss the causes of 

 sewage-sickness with special leference to adverse physical and 

 biological conditions. Certain physical conditions, such as the 

 deriocculation of the clay by the alkali of the sewage, lead to a 

 water-logging of the soil which enables certain large organisms to 

 grow freely, while the bacteria that induce decomposition are 

 injuriously affected. In addition to this, the large organisms 

 prey upon the bacteria. With this combination of factors, the 

 decomposition of the sewage stops, and the soil is said to be sick. 

 Upon resting the soil, the excess of water disappears, the condi- 

 tions become unfavourable to the larger organisms but favourable 

 to the bacteria, and the soil again becomes fit to receive sewage. 

 Extending the results obtained by them in the treatment of soils 

 by volatile disinfectants, they claim that a partially rested sewage- 

 soil, in which the protozoa have been destroyed by treatment 

 with toluol ov carbon bisulphide, is more effective as a filter than 

 an untreated soil, and that the soil does not so quickly lose its 

 efticiency. 



In my work upon soils, I have shown f that the numerical 

 increase of the bacteria is limited by the bacterial toxins and 

 fatty substances which are found normally in soils. The fatty 

 substances, which I have named collectively agricere, waterproof, 

 as it were, the particles of nitrogenous organic matter, and pre- 

 vent their rapid disintegration. When the soils are treated with 

 the volatile disinfectants, which are also fat-solvents, the water- 



* Journ. Soo. Chem. Ind. xxx.(1911), p. 471. 

 I These Proceedings, HUM, pHOS; 1911, p.()79. 



