454 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1953 



preservative into the agar medium. He proposed the use of thin plaques 

 of wood, measuring 3^ x 3 x 3 inches. These could be soaked to any re- 

 quired concentration of preservative and then tested by placing them 

 over wet filter paper in Petri dishes. The test specimen would be sup- 

 ported just above the wet filter paper on sterilized wood strips. Inocula- 

 tion was to be by the simple process of placing a small square of agar 

 plus the growing test fungus directly on the upper surface of the test 

 ''block." Similarity to natural conditions and the control of moisture 

 content of the wood were considered to be decided advantages for the 

 method. 



Cislak (see discussion of Snell and Shipley^^^) used similar plaques of 

 wood measuring 4x4 inches and about J^g-i^^ch thick for experiments 

 on evaporation and permanency of creosote. 



Rhodes, Roche and Gillander^" used blocks measuring 3^ x J.^ x 3 

 inches. 



The European standard^^' ^^ block measures 5 x 2.5 x 1.5 cm, with the 

 long axis in the direction of the grain. 



Schulze, Theden and Starfinger, in addition to the standard block, 

 used ''half" blocks, i.e., blocks measuring 5 x 2.5 x 0.75 cm. All factors 

 considered, they do not regard the thinner block as an advantage, and 

 they have held to the standard size.^ ^^^ 



Lutz^^ in 1935 suggested the use of 2 x 2 x 5 cm. blocks, with the long 

 sides dressed parallel to the fibers of the wood. He also used blocks 

 measuring 1 x 1 x 5 cm. 



Alliot^ favored blocks measuring 5.0 x 1.0 x 0.5 cm. in the longitudinal, 

 tangential and radial directions, respectively, for a French standard test. 



In his recent tests^^' ^^ Harrow has used IJ^ x ^^q x % inch blocks. 



Sedziak^"^ uses %-inch cubes cut from %-inch stakes after treatment. 



The National Wood Manufacturers' Association^"^ standard block size 

 is 1.25 inches on the radial surface, 1.75 inches on the tangential surface 

 and 0.25 inch thick, i.e., in the longitudinal direction of the grain. 



Various size blocks have been used at Madison in soil-block tests of 

 natural durability, but two sizes only have been employed commonly 

 since 1944 in the above mentioned soil-block tests and agar-block tests. 

 The soil-block is the ^-inch cube, generally drilled with a 3^-inch hole 

 in the center of a tangential face. The agar-block was cut with two broad 

 transverse surfaces measuring ^xl}^ inches, and with a distance along 

 the grain of only % inch; and it was not drilled.'*^ The Madison agar- 

 block is basically the same sort of a block as the one described in the 

 previous paragraph, and it resembles the Breazzano blocks as far as 

 maximum transverse surface exposure is concerned. 



