130 A MANUAL OV BACTERIOLOGY 



The first to notice this unfavorable effect of soil sterilization was 

 Dietrich/ who concluded that some poison was generated by the 

 action of heat upon the organic matter of the soil. Schulze ^ found 

 that the immediate effect of heat was injurious to bacteria as well as 

 to the higher plants. 



Koch and Ltlken' found that the application of heat produced 

 immediate injurious effects in soils, even though fertilizers were 

 applied in each case. The injurious effects were found to be un- 

 important if the plants were started in summer instead of early 

 spring. 



Lyon and Bizzell,* who also noted the immediate harmful effect of 

 heat, found that, upon standing, the quantity of soluble matter de- 

 creased, especially the total soluble nitrogen. The soluble organic 

 and inorganic matter decreased in about the same ratio. The growth 

 of wheat plants on steamed soil seemed to hasten its recovery from 

 the injurious effects of heating. The time required for the various 

 soils to recover from these effects was, with one exception, in the 

 order of their relative productiveness. 



The experiment of Pickering^ dealt with the effects of heated 

 soils upon seed germination and upon tree growth. He interpreted 

 his results to mean that the heat produced in the soil a nitrogenous 

 compound which was inhibitory to the germination of seeds. This 

 compound was sufficiently stable in solution for the extract of a 

 heated soil to affect a normal soil when added to the latter. 



The first successful attempt to show the chemical nature of the 

 changes in organic matter caused by heating soils is that of Schreiner 

 and Lathrop.^ Heating the soils in the autoclave for three hours at 

 about 135° C. produced an increase in water-soluble constituents and 

 an increase in acidity. At the same time ammonia and amines were 

 formed. By the process of heating, all the constituents isolated 

 from the unheated soil, except nucleic acid, were increased, and, 

 when not previously existing, xanthine, hypoxanthine, guanine, 

 cytosine, and arginine were formed. These compounds are decom- 

 position products of nucleic acid and protein material, and all are 

 beneficial to plant growth. 



1 Jahresber. Landw. Versuchs. Marburg, 1901-1902. Bied. Centralbl. 32 : 68. 1903. 



2 Jahresber. angew. Bot. 1 : 37. 1903. Centralbl. f. Bakt., 2te Abt., 2 : 716. 1903. 



3 Jour. Landw. 55 : 161. 1907. 



4 Bulletin JVb. 275. Cornell Exp. Sta., 1910. 



« Jour. Agr. Sci. 2 : 411. 1908. Ibid. 3 : 32. 1908. 



6 Bulletin No. 89. Bur. ol Soils. U. S. Dept. Agr., 1912. 



