THE TOXICITY TO FUNGI OF VARIOUS OILS AND SALTS. 15 



Petri-dish conditions, tests on its properties when injected into 

 wood should follow, under both laboratory and service conditions. 



Recently, an attempt has been made by a European investigator 

 (20) to correlate Petri-dish results directly with service values- 

 First, the preservatives were grouped as nearly as possible according 

 to their permanence in wood. Then, knowing the average length 

 of life of the treated timbers, the amount of preservative necessary 

 to inject to give this life, and the toxic point of the substances as 

 indicated by Petri-dish tests, a curve was plotted using the first fac- 

 tor as the axis of ordinates and the ratio existing between the second 

 two as the axis of abscissas. From this curve the investigator would 

 predict the possible service value of any new preservative of like per- 

 manence in wood merely from the known Petri-dish ratio by locating 

 the point at which its ordinate intersects the standard curve. 



Such mathematical calculations are interesting, but must neces- 

 sarily be very limited in their application, since such variables as 

 the solubility and volatility of the preservatives, the nature of the 

 timber treated, and the soil and weather conditions to which the 

 treated wood is exposed must necessarily exert a great influence on 

 the length of the life of the material. 



At the Forest-Products Laboratory, 2,400 Petri-dish tests have 

 been made to date on 54 different substances; however, not all are 

 sufficiently complete to be reported. These include a few water- 

 soluble salts, but in the main they comprise various oils and tars. 

 These preservatives have been for the most part submitted by 

 American and European cooperators interested in having the sub- 

 stances examined. 



The tests were conducted using two wood-destroying organisms, 

 Fomes annosus Fr. and Fomes pinicola (Sw.) Fr., which have a wide 

 American and European distribution and are very important in the 

 decay of wood, particularly coniferous timber. The former is 

 undoubtedly the most serious fungus of coniferous mine timbers 

 in the United States. 



In general, the molds used by other investigators may be con- 

 sidered more resistant than the true wood-destroying fungi, but 

 the writers have considered it advisable to use only wood-destroy- 

 ing forms, in order to eliminate any possibly erroneous inferences. 



METHODS OF TESTING TOXICITY. 



The method of conducting the tests was in principle the same as 

 that used by other investigators, merely involving the mixing of the 

 various preservatives in definite proportions with media nutrient to 

 fungi. However, an attempt was made to refine the methods as 

 far as possible, so as to eliminate certain sources of error to which 

 attention has already been called. 



