WOOD SOIL COXTACT CrLTCRE TECIIXIQUE 12.? 



the effect of the preservative or fungicide will be obscured. When the 

 sapwood-water method^ was published, comparison between it and the 

 kolle flask method showed that the wood-water method had certain 

 advantages. 



Comparing the method of soil contact with that of soil burial, the principal 

 point of diflference is that a pure culture is used in the soil contact method 

 and a mixed culture is used in the soil burial method. Common to both 

 are the moisture-regulating and nutrient properties of the soil. Since the 

 microbial activity of unsterile soil is diverse, depending on the type and 

 source of soil, uniform results from soil burial could not be expected. \\ hen 

 wood specimens were exposed individually in bottles of non-sterile soil in 

 the laborator}', the amount of decay after 12 weeks' exposure was less than 

 10% for all specimens. The results were similar to those obtained by the 

 exposure of untreated wood out-of-doors at Gulfport, Mississippi, for the 

 two-month period (Fig. 5). Since decay-producing organisms were shown 

 to be present, the other organisms in the soil must have interfered with the 

 growth of the wood-destroying fungi. The antagonism between the wood- 

 destroying fungus Lentimis lepideiis and a contamination is shown in Fig. 6. 



The soil-contact technique instead of the soil burial method has been 

 used extensively to test cotton fabric, thread, paper, jute, fibers, and a 

 variety of other materials. The organisms have been varied according to 

 their occurrence on the particular substrate in nature. The fungi Chae- 

 tomium globosum, Aspergillus uiger, Stachybotrys atra, Stysaniis media, and 

 Metarrhizium have been established with excellent results on a substrate 

 of cloth when testing fabric. The loss in tensile strength of an unprotected 

 cotton thread which had an initial absolute pull of 30 pounds was 90-100% 

 after two weeks' exposure to Chaetomium globosum. Treated threads or 

 other cellulosic materials may be tested as satisfactorily as treated wood. 



Examination of numerous reports from soil burial studies of treated textiles 

 indicates that organisms which tolerate certain types of chemicals become 

 dominant in the test beds. As a result, a preservative which shows great 

 promise initially may suddently fail when the test is repeated. If a pure 

 culture technique were used, a better evaluation of the preservative would be 

 possible. 



Similarly the controversies which have arisen over the ability of certain 

 fungi to destroy cellulose could be resolved by using the suitable cellulose 

 soil technique. At least there is very good evidence that man>- of the en- 

 vironmental variations affecting decay are at or near the optimum. 



Toxicity Tests 

 In the toxicity tests which follow, petri dish results are given for several 

 compounds, soil contact test results are given for compounds not readily 



