154 



DISCOVERY 



forms the basis of some soil insecticides. The full 

 utility of this compound, also, is impaired bj' the fact 



So 



I 



$30 



3 20 



CC 



?/0 



8 



lb 



5o 



Fig. t.— DIS.^PPEARANXE OF PHENOI, FROJI MA>"VEED SGIT.. 

 S — Disappearance from sterilised soil. 



A, B, C = Disappearance of tbree successive doses from a single soil sample. 

 (.\fter Sen Gupta.) 



that it disappears too rapidly when added to the soil. 

 The cause of the disappearance of these antiseptics 

 from the soil was therefore studied at Rothamsted 

 with the object of preventing their rapid loss, and 

 so prolonging their antiseptic action. 



A study of the disappearance of pihenol, from the 

 chemical point of view, was made by Sen Gupta, who 

 found evidence that two causative factors were in- 

 volved, a purely chemical or physical cause, and a 

 biological cause. If a dose of phenol be added to soil 

 in which all the bacteria have been killed by treat- 

 ment with mercuric chloride, the disappearance is at 

 first rapid, but soon takes place at a slower rate. 

 Evidence has been adduced that this disappearance 

 is due to the reaction of the phenol with a chemical 

 substance in the soil. In normal unsterilised soil, on 

 the other hand, the disappearance of the same dose 

 of phenol is much more rapid and follows a less regular 

 course. A second factor causing the disappearance 

 has therefore been removed by the sterilisation. The 

 probabilitj- that this factor is biological is shown by 

 the fact that if three successive doses of phenol be 

 added to the same sample of soil, the second dose 

 disappears more rapidly than the first, and the third 

 more rapidly than the second. This is what would be 

 expected if the disappearance were due to organisms 

 multiplying in the soil following the addition of the 

 phenol, but it is very hard to explain on the supposi- 

 tion that the disappearance is purely chemical or 

 physical. The curves in Fig. i show graphically this 

 accelerated loss. 



The Function of the Bacterium 



Evidence of this type has led the Bacteriology 

 Department at Rothamsted to search for phenol- and 

 cresol-destroying bacteria in the soil. The existence 

 in nature of certain bacteria capable of attacking 

 phenol was already' known. On sewage filters thr 

 phenol, which is known to be formed by bacteria, 

 does not accumulate, and this fact led Fowler, Ardern, 

 and Lockett in 1910 to study the subject of its dis- 

 appearance. They were successful in isolating an 

 organism capable, in pure culture, of feeding upon 

 phenoL Later, Wagner in Germany isolated from 

 various sources bacteria which could utilise benzene 

 ring compounds, a class to which naphthalene belongs, 

 as supplies of energy. 



An examination of the soils around Rothamsted 

 showed that they contained soil bacteria capable of 

 attacking phenol, cresol, toluene, and naphthalene in 

 pure culture. The organisms that have been isolated 

 can use some or all of these compounds as the source of 

 energy for carrying out their life-processes, and are 

 able to grow rapidly in a solution containing the anti- 

 septic and no other food supply than inorganic salts. 

 Since the phenols are strongly antiseptic in their 

 action on most bacteria, it is especially remarkable 

 that organisms commonly occur in the soil that can 

 feed on these compounds. The decomposition of 

 naphthalene by soil bacteria is even more remarkable, 

 since it is inconceivable that the bacteria can meet with 

 it to any significant extent in a state of nature. 



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Sc«Le I 'ou. 



FIC. ;.— B.\CTERI.i WHICH DECOMPOSE ANTISEPTICS GIvOUP D. 



X r.oor. I 



Having found that bacteria capable of attacking 1 

 organic antiseptics occurred in Rothamsted soil, it 

 was necessary to decide, firstly, \\^hether similar- 



