70 BULLETIN 1036, U. S. DEPARTMENT OF AGRICULTURE. 



pounds, the toxicity increases with molecular weight and with rise 

 in boiling point. Russell and Pendleton (32) have shown that both 

 pyridine and quinoline are valuable for soil sterilization. 



It is realized that these tests on the various constituents of coal-tar 

 creosotes are not conclusive proof of the antiseptic action of these 

 materials when they are applied to timber-destroying fungi. The 

 tests do at least point out the way in which it is most probable that 

 creosote produces its toxic effect, and it might reasonably be assumed 

 that the various classesof compounds, when applied to fungi, will 

 behave in much the same way as they did in the tests in which they 

 were applied to various other lower organisms. This will be the more 

 probable if the general conclusion can be substantiated by a consider- 

 able amount of data. Certain tests now being made at the Forest 

 Products Laboratory show that the tar acids are extremely toxic to 

 timber-destroying fungi; that the tar bases are as toxic to these 

 fungi, if not more so; and that the higher hydrocarbons under test 

 have at best a slight toxicity. It seems, therefore, that the conclusion 

 is justified that creosote oil in a large measure owes its toxicity 

 against timber-destroying fungi to the tar acids and tar bases which 

 form a small part of its composition, the rest of the toxic effects 

 being caused by the light oil. The heavier oils have but little toxic 

 value for this purpose. This conclusion is further brought out by 

 the curve (fig. 36) showing the toxicity of coal-tar creosote plotted 

 against its volatility at 275° C. 



TESTS ON MARINE BORERS. 



Practically the only work of this nature on the toxicity of creosote 

 and its constituents toward the marine borer that has been published 

 is that of Dr. Shackell (40). He showed that the phenols were 

 extremely poisonous to the Xylotrya, but that the hydrocarbons, 

 naphthalene, and anthracene could apparently be taken in and 

 ejected from the body of this marine borer with no ill effects upon the 

 animal. In conformity with this result, he found that the lower 

 fractions of creosote are more toxic, and that, as the boiling points of 

 the fractions increase, the toxicities decrease. 



COMPARISON WITH SERVICE TESTS. 



It is of considerable interest to compare the results of toxicity 

 tests with service tests on the same material. Fortunately, there is 

 in the- Forest Products Laboratory a series of fractions of coal-tar 

 creosotes which have been tested by the Petri-dish tests for fungi, 

 by laboratory tests for Xylotrya, and by service tests as piling. 

 Table 26 shows such a comparison. 



