A Wood Soil Contact Culture Technique for Laboratory Study 

 of Wood-Destroying Fungi, Wood Decay and Wood Preservation 



By JOHN LEUTRITZ, JR. 



Limitations imposed by other biologica! test methods have largely been over- 

 come by usinp autoclaved top soil for the substrate and pure cultures of the decay 

 organisms. The use of soil was the direct result of observations on the rapid 

 decay of wood in contact with soil in laboratory termite colonies. 



Development of a wood-soil contact culture technique as a result cf these 

 observations furnished an excellent laboratory tool for further research on the 

 biological factors promoting and the preservative compounds proposed for pre- 

 venting decay. Research on the factors promoting decay showed not only that 

 the average top soil furnishes nutrients and nutrilites in the quantity and propor- 

 tion highly favorable to many decay organisms but also an effective means of 

 regulating the water content of wood or cellulose during the decay period. 



Comparisons between laboratory and field results showed the amount of decav 

 obtained by the wood soil contact technique to be more rapid and uniform than 

 decay in the field. The severity of the exposure in the laboratory ensures imme- 

 diate eliminations of compounds unworthy of further more expensive field 

 studies and evaluates compounds in the same order of effectiveness. 



Comparisons and evaluation of wcod and cellulose preservatives plus artificial 

 weathering cycles followed by exposure to the method will provide valuable infor- 

 mation on initial toxicity and permanence thereby affording a sound basis for the 

 engineering selection of preservatives for a variety of purposes. 



LABORATORY tests for evaluating fungicides are often used as a means 

 of predicting field results and for investigating the action of cellulose 

 and wood-destroying fungi. Of the several laboratory procedures hitherto 

 devised for these purposes, however, none has been entirely adequate. 

 This has led to incorrect interpretation of laboratory assays of fungicidal 

 compounds, with attendant misapplication of preservatives. The con- 

 fusion and misunderstanding concerning the use of preservatives have been 

 further increased by the misapplication of the laboratory procedures them- 

 selves. A brief review and explanation of some procedures and their applica- 

 tion will clarify these statements. 



Minute quantities of toxic agents and growth-promoting substances 

 which are not readily detected by known chemical analyses may be deter- 

 mined by bio assay methods, the value of which depends upon a prior 

 determination of the reaction of one or more organisms to known quantities 

 of these substances. Another bio assay is the so-called "acceptance test" 

 for fungicides, by which the fungus resistant qualities of materials impreg- 

 nated with fungicides may be determined. Since fungus resistant qualities 

 are the primary concern in such a test, the identity and quantity of the 

 preservative are of only incidental interest. However, the identity, fungus- 

 proof qualities and quantity of fungicidal compounds are important when 



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