124 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1953 



indicate how these results may possibly be correlated with test plot and 

 field experience. 



A SHORT HISTORY OF THE DEVELOPMENT OF LABORATORY EVALUATION 

 PROCEDURES 



The practice of laboratory evaluation of wood preservatives developed 

 along different lines in Europe and in the United States. Here the Petri 

 dish method was the early favorite. ^^' ^°° The basic scheme of this test is 

 to use agar culture media containing gradient concentrations of the 

 preservative material to be tested, and to employ various easily grown 

 test fungi as indicators of inhibiting or lethal doses. The same scheme is 

 employed mth stoppered Erlenmeyer flasks. The fungus now known as 

 Madison 517, formerly referred to as Fomes annosus, has been used most 

 frequently as the standard test organism although other fungi were also 

 used.^°^ 



In the culture phase of the European standard agar-block method^^ 

 the test fungi are grown in Kolle flasks on a malt agar medium. The 

 impregnated wood test blocks are supported on glass ''benches" juSt 

 above the surface of the agar and the growing test fungus. Wood pulp 

 or paper boards saturated with malt extract are used by some investi- 

 gators^' ^ ^^^ in place of the agar medium alone. Generally an untreated 

 block and a treated block are placed together in the same flask. 



The concept of a test for wood preservatives that motivated the 

 proponents of the German agar-block method was broad enough to 

 include selection of the test blocks and test fungi, treatment and hand- 

 ling procedures except weathering tests, culture technique, determination 

 of the protection boundary, and directions for reporting the results. 

 Differences in the behavior of water solutions of single chemical com- 

 pounds such as sodium fluoride, and of volatile oily preservatives such 

 as the creosotes were recognized; and provision was made for dealing 

 with both types of materials. 



The formahzing of both the Petri dish agar method in the United 

 States and of the agar-block method in Europe developed as a result of 

 conferences called by Dr. Hermann von Schrenk, the first in St. Louis 

 in 1929, and the second in BerUn in 1930. The Laboratories' representa- 

 tives at the St. Louis conference were the writer and R. E. Waterman. 

 The action taken at St. Louis was published by Schmitz in 1930.^°° 



In a previous paper'' about a year earlier, Schmitz had discussed 

 various laboratory test procedures, and had offered an ''improvement" 

 in the Petri dish technique based on the idea of preventing evaporation 

 of volatile materials. Some of his statements at that time now seem by 



