810 CONTRIBUTIONS TO OUR KNOWLEDGE OF SOIL-FERTILITY, 



fallowing; but more recently they consider* that the toxins arise 

 from the action of bacteria upon the residues left by the crop in. 

 the field-soil. 



Believing that, in the soil, there are bacterial toxins, and that 

 much had yet to be discovered concerning them, and also that 

 the importance of the protozoal hypothesis had been exaggerated,. 

 1 began this work upon soils. 



By the use of soil-extracts filtered through porcelain, I have 

 found that hacteriotoxins are normally present in soils, and that 

 these either kill off or restrict the growth of bacteria which had 

 been added. The result is entirely a question of the amount of 

 toxin, and also of the kind of bacteria. Some bacteria are more 

 sensitive to this toxin than others. The toxin is destroyed, 

 partially or entirely by heat, by the action of aqueous solutions, 

 in both of which the time-factor has an influence, and by the 

 action of sunlight. The solubility of the toxin varies according 

 to the salts present in aqueous solutions; it appears to be more 

 soluble in solutions of magnesium sulphate, potassium sulphate,., 

 and sodium chloride than in water, in the order named. 



A factor, which hitherto lias been unnoticed, has a certain 

 bearing upon questions affecting soil-fertility. This is the- 

 waxy or fatty substance present in all soils. It consists of a 

 mixture of saponifiable and unsaponitiable bodies, and, by water- 

 proofing the soil-particles, it limits the free solution of nutritive 

 matter. It is undoubtedly largely derived from vegetable 

 remains, and is probably the "matter soluble in ether" of 

 vegetable residues. The distribution of this " agricere " is 

 altered by the soil being treated with wax-solvents, such as the 

 volatile disinfectants; and is more or less segregated, not only 

 locally on the soil-particles, but also in the layers of the soil. 

 Thus the action of the disinfectants is partially explained. The 

 full explanation, however, is not yet evident, 



Russell and Hutchinson, by excluding the presence of soil 

 toxins, came to the conclusion that the phagocytic protozoa were 



Chem. Soc. London, Annual Report, 1908, p. 246. 



