198 



BELL SYSTEM TECHNICAL JOURNAL 



A New Assay Method 

 Both the petri dish and kolle flask methods had shown definite 

 limitations, and it became apparent that further experimentation on a 

 laboratory assay-method should be directed along somewhat different 

 lines. By chance a few treated pieces which had been removed 

 unscathed after a routine exposure in the kolle flask, were dropped on 

 a beakerful of moist wood heavily infected with a wood-destroying 

 fungus. The beaker was merely covered with a watch-glass and set 

 aside. Growth progressed over the treated blocks with unexpected 

 rapidity and vigor, and when removed at the end of three months, 

 the specimens were found to be severely decayed. Occasional results 

 of this character were so encouraging that efforts were renewed to 



Fig. 3 — Apparatus required for modified wood-block method of assay. 



develop a technique which would incorporate the use of wood as a 

 secondary substrate together with more favorable moisture control. 

 Experimentation had demonstrated that the amount of moisture in 

 the wood block should be slightly above fibre saturation for optimum 

 growth of the fungus. Inoculated wood placed in air at 100 per cent 

 relative humidity will rot but slowly while too much moisture de- 

 celerates and even inactivates the fungal metabolism. The problem 

 therefore was to bring about these optimum decay conditions with 

 low-priced, easily handled equipment. The test in its present state 

 of evolution is inexpensive, easy to manipulate and capable of increased 

 uniformity due to better regulated moisture conditions. The only 



