58 The Non-pershtence of Bacterlo-toxins in the Soil 



subjected to heat, distinctly turbid owing to the formation of a finely 

 divided yellowish brown precipitate, which was found on examination 

 to contain appreciable c^uantities of iron. The occurrence of such 

 compounds in saline extracts of acid soils has been frequently noted 

 and has been the subject of investigation by Daikuhara. The amount 

 of interaction which takes place between the soil and neutral salt 

 solutions appears to be determined by the amount of adsorptively 

 un.saturated substances, by the concentration of the solution, by the 

 salt used, and results in the passage of appreciable quantities of iron 

 and ahuninia compounds into acid solution. The effect of these com- 

 pounds on introduced organisms has not yet been ascertained, but it is 

 noteworthy that the only soil found by us to yield acid extracts, also 

 exhibited effects corresponding to those which were interpreted by 

 Greig Smith as being due to toxins. How far these two facts are directly 

 connected must for the present remain an open question, but it might 

 here be mentioned that Greig Smith records the generally acid character 

 of Australian soils but without attempting to correlate soil reaction and 

 toxicity of the extracts. It is possibly in some such direction that an 

 explanation of the observed phenomena may be sought, but in any case 

 the use of saline solutions for the preparation of the extracts by intro- 

 ducing the interchange of bases appears to complicate the question at 

 issue. 



As this soil was the only one of the seven examined which gave 

 extracts indicative of the presence of "toxins," it appeared of interest 

 to determine what relation, if any, existed between acidity and "toxicity." 

 With this in view two equal samples of 80 grams of soil were digested 

 (a) as control, in ]6()Uc.c. of water saturated with carbon dioxide, and 

 {b) in 1600 c.c. of a solution of calcium carbonate likewise in water 

 saturated with carbon dioxide. After 4 hours' digestion the soils were 

 dried on a Buchner filter and in case the bacterial flora should have been 

 adversely affected by exposure to the carbon dioxide, the two portions 

 of soil were inoculated by means of an aqueous extract of normal soil. 

 The soils were then incubated and examined after 24 and 48 hours. 

 The results of enumerations were as follows: 



Bacteria per gram of soil after 



The rapid increase in the numbers of bacteria in the soil saturated 

 with calcium carbonate cannot be attributed to the extraction of toxins 



