36 
BULLETIN 227, U. S. DEPARTMENT OF AGRICULTURE. 
Temperature is also an elemental factor in the growth of f ungi, and 
there is an optimum for each organism, often lying within a very 
narrow range. The growth activities of fungi probably bear a close 
relation to the resistance offered toward toxic agents. 
The toxic elements or radicals in a compound are often difficult to 
determine. In the case of heavy metallic salts, it is the metal ion; 
in the case of strong inorganic acids, the hydrogen ion is said to be 
the important element; in the fluorin compounds, fluorin is the 
determining agent; in the case of certain phenols, the introduction 
of halogen, alkyl, or nitro groups is said to increase toxicity.. Even 
in the case of isomeric compounds the grouping of the radicals plays 
an important part. 
The Petri-dish method of determining the toxicity of a substance 
offers a ready procedure which gives indicatory results in a short time. 
On account of certain sources of error, some inaccuracies must be 
admitted, although the methods employed by the writers obviate 
many of these. 
The results of tests on 18 wood preservatives at the Forest-Products 
Laboratory, against two wood-destroying fungi, Fomes annosus Fr. 
and F. pinicola (Sw.) Fr., are given. The preservatives act in a 
considerably different manner on these two organisms, the former 
being, as a rule, far more resistant. 
The tests show that for these two organisms the following quan- 
tities of preservative per cubic foot of culture medium used are suf- 
ficient to inhibit all growth: 
FOE FOMES ANNOSUS. 
Pounds. 
Coal-tar creosote, Fraction II 0. 14 
Sodium fluorid .16 
Cresol calcium 0. 09- . 18 
Coal-tar creosote: 
Fraction I .19 
Fraction III .20 
Zinc chlorid .31 
Coal-tar creosote, grade C... .34 
Water-gas tar distillate (sp. 
gr. 0.995) .41 
Wood creosote .41 
Hardwood tar .78 
Coal-tar creosote, Fraction IV 2. 06 
S. P. F. carbolineum 2.8 
Avenarius carbolineum 3. 27 
Coal-tar creosote, Fraction V. 20. 59 
Copperized oil 25 
United Gas Improvement 
Co., 1.07 oil Over 25 
None-Such Special Over 25 
Sap wood antiseptic Over 25 
FOR FOMES PINICOLA. 
Pounds. 
Coal-tar creosote: 
Fraction III 0.08 
Fraction IY .08 
Fraction II .09 
Sodium fluorid .09 
Wood creosote .13 
Coal-tar creosote: 
Grade C .14 
Fraction I .14 
Avenarius carbolineum .19 
Zinc chlorid .47 
Hardwood tar .47 
Coal-tar creosote, Fraction V 4. 87 
Copperized oil Over 25 
United Gas Improvement 
Co., 1.07 oil Over 25 
None-Such Special Over 25 
