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vanillin were added. From time to lime the number of 

 microorganisms developing in the pots was determined 

 by the methods described by Brown (1) using his al- 

 bumen agar. Each soil was plated in duplicate using 

 dilutions of 1-20,000 and 1-200,000 as described by 

 Brown. The number of microorganisms developing in 

 the pots is given in Table 1. 



TABLE 1 



Micoorganisms in Millions per gm. of Air Dry Soil. 



Soil Potted June 5th, Vanillin Added July 5. 



The data in Table 1 indicate that the persistence of 

 vanillin in the Arlington soil is due to some condition 

 or conditions which prevent the destructive action on 

 vanillin of the vanillin-destroying bacteria. As was 

 found before (6) the addition of vanillin to the Alaba- 

 ma soil first produces a decrease in the number of 

 microorganisms which will develop on Brown's al- 

 bumen agar. This decrease is followed by an increase 

 in which the numbers far exceed those present lu the 

 normal soil. There is then a return to normal. In the 

 Arlington soil, however, no such phenomenon occurs. 

 The addition of vanillin produces a marked decrease in 

 the numbers but this is not followed by any increase. 

 In fact, as far as bacteria are concerned, the upper lay- 

 ers of soil remain practically sterile as the majority of 

 microorganisms indicated in the table as developing in 

 the vanillin treated Arlington soil were molds. Only 

 occasional bacterial colonies ap])eared on the plates 

 from these pots. Even the addition of a pure culture 

 of a bacterium known to destrov vanillin does not im- 



