4 president's address. 



Another investigation led to the elucidation of a pheno- 

 menon of general occurrence in the household. The ordinary 

 bath-sponge frequently becomes slimy from the action of 

 certain bacteria which attack the substance of the sponge, 

 converting it into slime. The nature of these microbes and of 

 the slime has been described by the Macleay Bacteriologist. 



The action of heat and of volatile disinfectants in increas- 

 ing the fertility of the soil has recently received attention 

 from those interested in agricultural science. The treatment 

 reduces the number of bactei'ia, but the rediiction is soon fol- 

 lowed by an increase much above the normal. The greater 

 increase means a greater decomposition of the organic matter 

 of the soil, and consequent greater production of food- 

 materials for the growing crop. Russell and the Rothamsted 

 school claim that the heat and disinfectants act solely by 

 destroying phagocytic protozoa, and that the removal of 

 these permits the bacteria to increase. They deny that soils 

 contain substances of the nature of toxins which are inimical 

 to the growth of bacteria. 



Believing that as soils are essentiallv a mixture of inert 

 and nutritive materials in which bacteria are growing, they 

 must contain toxic bacterial by-products. Dr. Greig-Smith 

 began a series of experiments with soils and soil-extracts. He 

 showed that extracts of soils, filtered through porcelain, do 

 contain substances toxic to bacteria. These toxins are de- 

 stroved by heat, by storage and by sixnlight. The behaviour 

 of heat explains the benefit obtained by heating soils, and 

 the action of sunlight shows that the toxin must be con- 

 sidered in questions relating to the fertilising effect of sun- 

 light upon soils. 



The Macleay Bacteriologist discovered in soil a siibstance 

 which has hitherto been disregarded. This is agricere, a 

 mixture of saponifiable and unsaponifiable fatty substances ; 

 it is soluble in fat-solvents such as chloroform, ether, carbon 

 bisulphide, etc. The volatile fat-solvents have, in this rela- 

 tion, been considered as disinfectants, and this has doubtless 

 obscured their real action upon the soil. The solvents dis- 

 solve the agricere, and carry it to the iippermost layers, 



