WOOD SOIL CONTACT CULTURE TECHNIQUE 111 ! 



to submerge the blocks completely when the air is admitted. Alter re- 

 maining in the solution for 5 minutes, the blocks are wiped superficially and 

 and weighed. This treated weight is used for calculation of the theoretical 

 retention according to the following formula: 



^ GC(62.4) 



in which R* = pounds of preservative per cubic foot of wood, G = gain in 

 weight in grams, C= grams of the preservative in 100 grams of solution, and 

 Y = volume of the test piece in cubic centimeters. When the solvent has 

 evaporated from the blocks, they are placed on racks, returned to the 

 humidity chamber and brought to constant weight. The difference be- 

 tween the humidity weights before and after treatment serves as the basis 

 for calculating the actual retention, and the final equilibrium weight is used 

 also as the initial weight of the treated block before exposure to the fungus. 



The cross-section side of the blocks is placed in contact with the vigor- 

 ously growing mycelia of the sapwood culture which in turn is in contact 

 with the soil. For each concentration of preservative, three treated blocks 

 and three untreated control blocks are exposed to each species of fungus. 

 The bottles are recapped and place in an incubator or constant temperature 

 room at 26°-28° C. with a relative humidity of 85-95%. 



Exposure of the blocks to the fungus for from twelve to twenty-four weeks 

 gives satisfactory- results. If a sufficient number of treated specimens 

 is exposed to the same organism, one or two specimens may be removed 

 at the end of twelve weeks; and if considerable decay has taken place, 

 the test may be concluded. At the end of the exposure period the blocks 

 are brushed free of mycelia and imm.ediately weighed to determine their 

 moisture content. The blocks are then allowed to stand in the room until 

 dry, after which they are again transferred to the humid chamber (tem- 

 perature 30°C., relative humidity 76%) for two-three days until a con- 

 stant weight is attained. 



In the toxicity work reported in this paper an untreated reference block 

 was added to each test bottle. If a large number of assays are contemplated, 

 the number of weighings may be reduced by eliminating the untreated 

 blocks except for occasional reference purposes. The reduction in the num- 

 ber of reference blocks may be accomplished by establishing a decay norm 

 for each test organism. This norm would be based on data similar to that 

 used in Fig. 1 except that the procedure would be the same as that described 

 for treated blocks. Comparison of the percentage weight loss due to decay 



Kilograms 

 * To express the retention metrically R X 16.018 — ^^j^j^ meter 



