191 0] SOILS — FERTILIZERS. 23 



The non-persistence of bacterio-toxins in the soil, H. B. Hi.n m.vsox and 

 A. C. Tii.\ym:\ (./our. Ayr. Sci. [England], 9 (1918), No. 1, pp. ',.: 62, /"/<. ',)■— 

 Investigations are described which were undertaken at Rothamsted with seven 

 different soils in an effort to ascertain the validity of Greig-Smlth's claim that 

 the effect of partial sterilization may be due to the destruction of bacterial toxins 

 in the soil (E. S. EL, 25, p. 214). The studies embraced observations on the 

 rate of growth of Bacillus proiligiosus, and also, in the case of two soils, of B. 

 fluorescent liquefaciens in the treated and untreated extracts of the different 

 soils as compared with the rate of growth in a standard physiological salt 

 solution. The treatments included beating the extracts to 94° C. for one hour, 

 partially sterilizing the soil with toluene, and adding peptone representing six 

 parts of nitrogen per million of extract to untreated soil extract which had been 

 boiled. Bacterial counts were made directly after inoculation and 4, 8, 24, 48, 

 and 72 hours later. The behavior of B. prodiyiosus toward its own growth 

 products was also studied. The results obtained have been summarized as 

 follows : 



The untreated extracts of the soils varied widely in their suitability for the 

 growth of B. prodigt08U8. In some instances vigorous growth occurred, while 

 in others the numbers of introduced organisms fell to a minimum. Treatment of 

 the extracts by heat (supposed to result in the destruction of " toxins ") invaria- 

 bly led to still further bacterial decreases, while extracts of soils treated with 

 antiseptics (which are not supposed to destroy toxins) were on the whole more 

 favorable for growth than those of untreated soils. Such extracts were found 

 to have appreciably more organic nitrogen compounds than extracts of untreated 

 soils. The addition of minute quantities of peptone to unsuitable extracts 

 sufficed to convert them into favorable media. 



Extracts of the two poorest untreated soils were tested with B. fluorcsccns 

 liquefaciens, but no evidence of toxicity could be obtained, growth being very 

 abundant. It is concluded that results obtained by the use of an extraneous 

 organism, such as B. prodigiosus, must be accepted with reserve. The curve of 

 diminished numbers of bacteria in poor untreated soil extracts was practically 

 identical with that obtained when bacteria were introduced into pure salt 

 solutions, the decreases being symptomatic of starvation. 



The only soil which gave extracts similar in behavior to those reported by 

 Greig-Smith was an acid heath soil. The value of the extract of this soil was 

 distinctly increased after the extract had been subjected to heat. The acid iron 

 and alumina compounds which were removed from the soil by the action of the 

 saline solution were also thrown out of action. The "toxicity" of this soil was 

 found to be rapidly (within 24 hours) and effectively removed by treatment with 

 calcium carbonate. 



Alternate inoculation and removal of the bacterial growth by filtration 

 rapidly produced an extract unfavorable for the growth of B. prodigiosus, due 

 in part to the impoverishment of the extract in food material and also to the 

 formation of some substance inimical to growth. This body was capable of 

 passage through a porcelain filter and was heat stable, and therefore appeared 

 to have little in common with the inhibitory bodies described by Rahn as occur- 

 ring in cultures of organisms, such as B. fluorescens liquefaciens or B. coli, nor 

 did it resemble in its relations to heat the toxins which are alleged to occur in 

 the soil. 



Although it is deemed possible under well-defined conditions to induce the 

 formation of bacterio-toxins in culture solutions, it is stated that there is no 

 evidence to show that these are likely to possess importance in the phenomena 

 of partial sterilization of soil. 



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