WOOD SOIL CONTACT CULTURE TECIINIOUE 10,3 



laboratory procedures are devised for comparing effectiveness in the develop- 

 ment of different preservatives. In addition, the cherrical and physical 

 properties of the different preservatives must be considered for the deter- 

 mination of their subsequent behavior when exposed to a variety of en- 

 vironmental conditions. Bio assays may thus be used for quantitative, 

 qualitative, compara:tive, or predictive purposes. 



In order to survey existing tests, it may be helpful to classify them. 

 There are three groups of rather ill-defined laboratory methods based en the 

 nutrient and physical properties of the substrate. The first group is com- 

 prised of those methods in which an agar or similar base is used. \'arious 

 nutrients or nutrilites* may be added to this base', and prior to inoculation 

 with one or more fungi the preservative may also be added. This group 

 includes the standard petri dish test described by Richards-, 1923, which 

 has had extensive use in the field of wood preservation. The carbohydrate 

 source in the standard petri dish method was malt sugar. Later, in response 

 to the requests by industry, Richards attempted to substitute wood flour 

 as the nutrient. However, the radial fungus growth used as the criterion 

 of toxicity was very sparse and thin and the substitution of wood flour for 

 sugar was discarded. It is of interest to record here that Richards also 

 summarized the previous work on toximetric tests of wood preservatives. 



The second group includes those methods in which the preservative is 

 added directly to a cellulose material before exposure to organisms. The 

 preserved material may be the only source of nutrient for the fungi, or a 

 piece of similar untreated material may be provided. Such a method is 

 described in a paper by Waterman, Leutritz and HilP, 1938. No agar is 

 used, and the untreated wood is supported over water by mechanical means. 

 When agar is used to support the preserved material and to supply water, 

 nutrients, nutrilites or combinations of each of these may be added to the 

 agar. This may be done in several ways, among which are the kolle flask 

 method for wood preservatives described by Falck', 1927, the standard 

 method of the American Society for Testing Materials for testing fabiics^, 

 1942, and the present Signal Corps test of fungicidal coatings", 1943. Of 

 these, the first two methods are used chiefly as "acceptance" tests by de- 

 termining the fungus proof qualities of fungicidally treated wood and fabrics. 

 They are also used in development work for comparison and for predicting 

 the field behavior of preservatives when supplemented by artificial weather- 

 ing cycles. The Signal Corps test is used as an acceptance test of fungi- 

 cidal coatings which are sprayed on electical equipment. Since the criterion 

 is the inhibition of fungus growth at some distance from a pa!)er impreg- 



* Nutrients here include the sugars and compounds used l)y the fungi foi food purjioscs, 

 and nutrilites will be referred to in this pa[)er as those compounds necessary to fungus 

 nutrition, such as vitamins, growth sut)stances and minerals, Williams, R. J., 1928. (See 

 Bibliography at end of this paper.) 



