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III. "Partial Sterilisation of Soil by Volatile and Non- 

 volatile Antiseptics:' WALTER Buddin. Journal of 

 Agricultural Science, 1914. 6, 417—451. 



Nearly all the antiseptics used cause increases in bacterial 

 numbers after treatment as Hiltner has already pointed out, and they 

 also mostly produce an initial increase in the amount of ammonia. 

 Here, however, the uniformity ceases, and closer examination shows 

 that two very distinct classes of antiseptics exist— 



(1) those which are completely volatile and disappear entirely 

 from the soil once their work is done ; 



(2) those which remain in the soil for a considerable period or 

 else leave decomposition products and so exert a prolonged action on 

 the bacterial flora and on the plant. 



1. — The easily volatile antiseptics are all similar in their action 

 but differ as regards their potency. When a particular strength is 

 reached all the usual partial sterilisation effects observed by Russell 

 and Hutchinson show up together : an initial depression in the 

 numbers of bacteria, the killing of all protozoa, except a few flag- 

 ellates, the killing of nitrifying organisms, and a small initial 

 production of ammonia ; followed later by a large sustained increase 

 in bacterial numbers and in the rate of production of ammonia. 

 The methods used for the examination of the soils did not disclose 

 any substantial difference in result with any higher dose once partial 

 sterilisation had occurred. On the other hand the weakest doses 

 have no effect on the numbers of bacteria occurring in the soil, nor 

 on the rate of production of ammonia and nitrate, and as far as can 

 be judged from the ordinary one per cent, hay infusion culture 

 method, no appreciable action on the protozoa. 



The investigation included a group of compounds so mild that 

 they can hardly be considered as antiseptics — the open chain hydro- 

 carbons. These give an initial depression in bacterial numbers and 

 a very distinct increase in the initial ammonia content, but nitrifying 

 organisms are not killed nor are the larger protozoa suppressed. 

 There is no distinct and permanent increase in the numbers of bac- 

 teria : there is, however, a marked increase in nitrate production. A 

 similar but weaker action occurs after merely spreading out the soil 

 in a thin layer for 24 hours so that it dries down on the average to 

 about five per cent, water. In this case there is after moistening a 

 similar increased rate of production of nitrate over that in the soil 

 which has been kept in a moist state after being bottled fairly fresh 

 from the field, although there is no noticeable effect on the numbers 

 of bacteria. The decreased action is indicated by the absence of 

 marked initial effects. 



2. — The non-volatile antiseptics all produce a permanent 

 depression in bacterial numbers with the highest doses. The more 

 potent such as quinone and hydroquinone show an initial depression 

 in numbers of bacteria developing on gelatine plates even with the 

 weakest dose used (approximately 0*05 per cent.), while the less 

 potent show no initial effects with such strengths excepting the 

 liberation of a small amount of ammonia. With all the antiseptics 

 the dose which is sufficient to produce the full initial depression in 

 numbers also kills the larger protozoa and checks the action of 

 nitrifying organisms. The traces of substance left behind in the 



