496 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1953 



preservative to use with a view to providing the necessary residual and 

 effective preservative. 



The agar-block tests are somewhat better in this respect. While addi- 

 tional proof is necessary the results of such tests may be good indices of 

 retention requirements for certain water-borne preservatives. The com- 

 parison of agar-block and soil-block tests made by Warner and Krause^^^ 

 is incomplete, and therefore somewhat unsatisfactory, particularly in 

 view of the title of their article. They do not follow through, and they 

 repeat some of the inferential objections raised by others as to the effect 

 of soil differences and methods of interpretation. The comparison by 

 Finholt et al^^' *^ is also inconclusive chiefly because of the nature and 

 design of their experiments. So also, but to a lesser degree, are the com- 

 parisons that one may draw from the first two papers on the soil-block 

 and agar-block tests from Madison, ' Avhich after all, were in the 

 nature of preliminary or reconnaisance studies, introducing the first 

 trials of an outdoor weathering technique, and developing the necessary 

 steps in the broader and more comprehensive plans followed later. 



Duncan has now brought out a full scale comprehensive study of the 

 agar-block and soil-block techniques, which, however, deals with oil 

 type preservatives only. She shows definitely — as was indicated in the 

 earlier Madison work — that the test fungi are more aggressive under 

 the more natural and more realistic environment of the soil-block cul- 

 tures. Definite evidence of the very important better control of moisture 

 content in the soil-block tests is presented. The soil-block thresholds for 

 the different preservatives are generally higher in the soil-block tests, 

 although the order of effectiveness is essentially the same. 



Sedziak's^^^ recent paper comparing results of his tests on buried 

 soil-blocks and results of tests by a soil-block technique approximate to 

 that used at Madison and at Bell Laboratories is not convincing with 

 respect to the implied superiority of the buried block method. His paper 

 covers work begun after the early soil-block was started at Bell Telephone 

 Laboratories, but before the extensive experiments at Madison were 

 initiated. Satisfactory comparison of the work of the Madison and Ot- 

 tawa laboratories is difficult because Sedziak has used a different set of 

 test organisms, including the European Coniophora cerebella for example, 

 and Lenzites sepiaria. which is apparently not a satisfactory discriminat- 

 ing organism for creosote and pentachlorophenol. He has omitted the 

 very critical Lentinus lepideus that has been employed at Madison since 

 1944. While he interprets threshold retentions for penta and for copper 

 naphthenate that are close to those obtained at Madison, the steps in 

 his gradient retentions leave one wishing that the Madison and Ottawa 



