36 



BULLETIN 227, U. S. DEPARTMENT OF AGRICULTURE. 



Temperature is also an elemental factor in the growth of fungi, 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 difhcult 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, Forties 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: 



FOR FOMES ANNOSUS. 



Pounds. 



Coal-tar creosote, Fraction II 0. 14 



Sodium fluoric! .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 



( ' oal-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 



Sapwood antiseptic Over 25 



FOR FOMES PINICOLA. 



Pounds. 

 Coal-tar creosote: 



Fraction III 0. 08 



Fraction IV .08 



Fraction II .09 



Sodium fluorid .09 



Wood creosote .13 



Coal-tar creosote: 



GradeC .14 



Fraction I .14 



Avenarius carbolineum .19 



Zinc chlorid .47 



Ilardwood tar .17 



Coal-tar creosote, Fraction A' 4. 87 



Copperized oil Over 25 



United Gas Improvement 



Co., 1.07 oil Over 25 



None-Such Special Over 25 



