760 PRINCIPLES OF SOIL MICROBIOLOGY 



substances (dihydroxy-stearic acid, etc.) which are distinctly injurious 

 to crop growth. Livingston 08 regards the general hypothesis that 

 unproductiveness of agricultural soils as due frequently to soil toxins 

 as well established and generally accepted. 



According to Greig-Smith, 69 no one phenomenon can explain the cause 

 of the enhanced fertility of soils treated with volatile antiseptics. 

 Bacteria growing in any culture medium produce injurious or toxic 

 products, which check and inhibit their further growth. These toxins 

 may be in the nature of lysins, acids, accumulated by-products, etc. 

 Soil extract filtered through porcelain was found to have a destructive 

 influence upon Bad. prodigiosum, while the same extract heated and 

 treated by sunlight or allowed to stand in aqueous solution stimulated 

 bacterial growth. 



Greig-Smith considered that, in addition to the toxic substances, 

 the soil contains a mixture of fatty substances {agricere) derived from 

 plant material. These fats are not readily acted upon by microorgan- 

 isms and finally cover and inpregnate the residual organic matter. 

 Volatile antiseptics, being fat solvents, dissolve the agricere, which is 

 either carried toward the surface of the soil or is segregated upon the 

 points and angles of the individual soil particles. This was believed 

 to be the cause of the favorable influence of the action of antiseptics 

 upon bacterial growth and activities. When the soil fats are removed 

 or segregated, the soluble matter diffuses out more readily from the 

 soil particles and serves as a source of food for microorganisms. 70 



Treatment with volatile antiseptics was found to induce an increased 

 growth of bacteria in soils in which the protozoa have been destroyed 

 by moist or dry heat at 65° to 75°C. It was suggested, therefore, that 

 two factors influence bacterial activities in the soil, one of which is a 

 bacteriotoxin and which is destroyed by heat, and the other a soil 

 fat or wax, which is dissolved by volatile antiseptics. According to 

 Hutchinson, 70a the formation of toxic substances depends upon the 

 existence of anaerobic conditions due to water logging; when organic 



68 Livingston, B. E. Palladin's Plant Physiology. 1st Ed. 1918, p. 93. 



69 Greig-Smith, R. The agricere and the bacteriotoxins of the soil. Centrbl. 

 Bakt. I., 34: 224-226. 1912; Proc. Linn. Soc. N. S. Wales., 36: 679-699. 1911. 



70 Greig-Smith, R. Contributions to our knowledge of soil fertility. Proc. 

 Linn. Soc. N. S. Wales, 35: 808-822. 1910; 36: 679-699. 1911; 37: 238-243, 655- 

 672. 1912; 38: 725-746. 1913; 39: 839-850. 1914; 40: 631-645, 724-733. 1915; 

 42: 162-166. 1917; 43: 142-190. 1918. 



70a Hutchinson, C. M. Causes of infertility in soils in relation to bacterial 

 action. Agr. Jour. India, 21: 125-133. 1926. 



