6 PRESIDENTS ADDRESS. 



by both methods, whether heat were applied first or last. It 

 has been found that, while the results are similar in field-soils? 

 they are different in garden-soils. As one of the differences 

 between the two classes of soils is the fatty material removable 

 by disinfectants, it is not improbable that it plays a part in the 

 restriction of the natural fertility. The presence of bacterio- 

 toxins in soils has been denied by the Rothamsted investigators, 

 but there are many reasons why their presence may have been 

 overlooked. They are soluble in water, and are washed out of 

 the soil by rain. They are unstable, and are slowly destroyed 

 during dry weather. Although always present in varying 

 amount, the nutrients may so overshadow them, that their 

 presence may be unnoticed, until they are destroyed by some 

 aerent, such as heat, when an enhanced nutritive effect is obtained 

 from the soil-extracts. Furthermore, an appropiiate dilution, 

 generally equal parts of soil and water, is requisite to show an 

 optimum toxic effect. Toxic extracts can be obtained from soils 

 by noting these conditions, and a soil, originally with a pre- 

 ponderating amount of nutritive substances, may be made to 

 become toxic by simple incubation in the laboratory. While 

 the soil-toxins are destroyed by heat, those of the subsoil are not. 

 There are thus two classes of toxins in soils, a thermolabile in 

 the soil, and a thermostable in the subsoil. One would imagine 

 that the saturation of an organic manure, such as dried blood, 

 with paraffin or vaseline, would reduce the rate of decay. Labo- 

 ratory-tests have not borne this out, and the matter is under 

 investigation. The action of naphthalene upon soils was also 

 examined. This substance has recently been recommended for 

 increasing the fertility of horticultural soils. It was found that 

 while it increased the growth of bacteria, they were of a kind 

 which did not bring about the formation of ammonia from dried 

 blood. 



Dr. J. M. Petrie, Linnean Macleay Fellow in Biochemistry, 

 contributed two papers during the year, " Hydrocyanic Acid 

 in Plants. Part ii. Its Occurrence in the Grasses of New 

 South Wales," and " Note on the Occurrence of Strychnicine," 

 which will be found in the last Part of the Proceedings. In the 



