11 Feb., 1918.] Bacterial Toxins in Soils. 119 



weevils were not killed. It is only by adding lime at a high tempera- 

 ture under the conditions of Mr. Barrett's scheme that this is effected. 

 The tainted wheat lost nearly 20 per cent, upon being screened, and the 

 pronounced mousey and musty odour was considerably reduced, but 

 before the work of the lime could be completed it would require to be 

 applied fresh and hot, and left in contact for some months. The damp 

 wheat, although not so bad as the previous wheat, was yet incapable of 

 being converted into a wholesome article, though the lime had materially 

 reduced the smell and bacteria present. The mousey wheat was treated 

 with freshly ignited lime, and the results proved very satisfactory, show- 

 ing conclusively that the lime, to be effective, must be applied hot. The 

 bacteriological and chemical examinations made of the lime treated 

 wheat clearly indicate that considerable improvement has been effected. 

 The bulletin which gives full details of these experiments may be 

 obtained post free from the secretary of the Advisory Council, 314 

 Albert-sitreet, East Melbourne. 



BACTERIAL TOXINS IN SOILS.* 



Bt/ R. Greif/Sniiih, D.Sc, Macleai/ Bacteriologist to the Linnean 

 Society of New South Wales. 



If the soil-water is considered as a medium for the growth of 

 bacteria, it should contain not only the nutrients that favour bacterial 

 growth but also the waste products of their vital activity. And if we 

 reason from what we know about the growth of bacteria in other media, 

 we should expect that some of these waste products are injurious to 

 the bacteria producing them. Furthermore, in a mixed flora, certain 

 groups sliould produce injurious substances in greater amount, and 

 these should differ in degree in their action upon bacteria of their own 

 group or of other groups. For convenience, these injurioua substances 

 are called toxins. Certain investigators deny the presience of toxins 

 in soils, although they admit the presence of inhibiting substances. It 

 is difficult to account for the discrimination. 



The multiplication of bacteria in the soil will, among other con- 

 ditions depend upon the relative preponderance of the nutrients over 

 the toxins ; and, with the other conditions remaining constant, an 

 ultimate equilibrium should be established between the nutritive and 

 the toxic effects. An alteration of the other conditions will disturb the 

 equilibrium, and the bacteria will increase or decrease until another 

 balance is established. 



Russell and his colleagues believed that the bacterial imcrease in soils 

 was limited by phagocytic protozoa, and more recently they consider 

 that the limitation is occasioned by a something associated with the 

 presence of a mixed living fauna. Any treatment which destroys the 

 diversity of the fauna and at the same time kills off the nitrifying 

 organisms will insure an increased and sustained growth of bacteria. 



* Excerpt from a paper read before the AsricTiIture section of the British Association for the 

 Advancement of Science at its Australian meeting 1914. 



