Humphrey: Durability of American Woods 
83 
square and 2 inches long frorn clear material, free of defects. In 
selecting heart and sapwood close attention was paid to getting 
representative material. In order to determine the actual loss in 
weight from decay, the blocks were dried in a steam-heated oven 
for 48 hours at a temperature of 100° C., or close around that 
point, and then weighed to the nearest .01 of a gram. On the 
completion of the tests the blocks were again oven-dried in a 
similar manner, the resulting weights compared with the original, 
and the percentage loss, based on the dry weight of the sound 
material calculated. 
The flasks in which the experiments were carried out were pre- 
pared as follows: Culture blocks^ from i to 2 inches long and of a 
diameter sufficient to go through the neck of a wide-mouth flask 
were cut from hemlock, boiled to saturation in tap water, and 
given a preliminary sterilization of several hours at about 10 
pounds pressure in the autoclave. This was for the purpose of 
killing any latent fungi and of removing the excess water. On 
removing from the autoclave a layer of these blocks was placed 
in the bottom of each flask, resting on a layer of absorbent cotton^ 
saturated with water. The test blocks, usually ten different spe- 
cies to a flask, were then inserted in a dry condition, taking care 
to keep them well off the wet cotton. Another layer of hemlock 
culture blocks was then added to about three-fourths of the height 
of the flask, this being surmounted by another wad of saturated 
absorbent cotton. The flasks were then tightly plugged with 
cotton and sterilized in the autoclave, without pressure, for periods 
of 45, 30, and 30 minutes, respectively, on three successive days. 
After sterilization they were inoculated with a culture of Len- 
tinus lepideus, growing on a bean pod, by emptying the bean 
directly into the flask. When inoculating wood cultures it is 
quite essential to use a generous quantity of infecting material. 
The test blocks were grouped more or less according to their 
supposed durability, heartwood and sapwood samples in every 
1 The term “ culture blocks ” refers to the irregular hemlock blocks intro- 
duced into the flasks as a medium to support a vigorous growth of the fungus 
in order to secure a uniform and severe infection of the “ test blocks.” 
- In later work the cotton has been omitted, as the test blocks often became 
too wet. 
