FACTORS IN SOIL FERTILITY. 551 



The fact that toxin decays in aqueous solution is sufficient 

 to show the impossibility of obtaining information regarding 

 bacteriotoxins by growing seedlings in watery extracts of soils. 

 The decay of the toxin also occurs during the storage of the soil in 

 the air-dry condition. 



The toxin is destroyed by sunlight. A portion of soil was 

 exposed to the sun for 12 hours, while another portion beside it was 

 protected. The temperature of the former averaged 62°, the latter 

 42°, while the control in the laboratory averaged 20°. The ex- 

 tracts from these soils were seeded with Bac. prodigiosus dLn&incw- 



1,000 bacteria became 



Soil exposed to light 227,000 



,, protected from light .. .. .. 11 



,, in laboratory . . . . . . . . 9 



There can be no doubt that the recognised beneficial effect of 

 sunlight upon soil is caused by the destruction of toxin. 



The power of toxin is not diminished by salts, such as sodium 

 chloride, potassium sulphate or magnesium sulphate, for the toxic 

 effect of extracts of soil made with 0.5% solutions of these is very 

 pronounced. 



If a deep layer of garden soil is saturated with carbon bisulphide 

 and exposed to a current of air, a greenish-grey efflorescence may be 

 noted on the surface as the solvent evaporates. This is the soil-wax 

 or " agricere," which is doubtless the remains of the " ether-soluble 

 extract " of the residual organic matter of the soil. It consists of 

 saponifiable and unsaponifiable matter and acts as a protective 

 covering to the soil particles. It " waterproofs " the decomposable 

 organic matter. 



The action of the disinfectants is a double one ; they kill off 

 the less resistant bacteria, dissolve the agricere and carry it to the 

 surface of the soil. A redistribution is effected. Furthermore, on 

 the evaporation of the solvent, the agricere is deposited not uni- 

 formly over the soil, but at points on the surfaces of the particles in 

 the uppermost layers of the soil. This can easily be shown by 

 experiments on sand with a chloroform solution of a dark-coloured 

 agricere. There is the possibility that much of the toxin may be 

 deposited in a similar manner, but this has not yet been determined. 



The behaviour of heat and the volatile wax-solvents can now 

 be explained more completely than has hitherto been possible. 

 Heat destroys the soil toxin and the less resistant bacteria. Doubt- 

 less there are other effects produced, but I believe they are of minor 

 importance. Upon moistening the soil, the more resistant bacteria 

 multiply and become more numerous than before on account of the 

 absence of soil bacteriotoxins. 



The disinfectants, while destroying the comparatively inactive 

 bacteria, simply remove the waterproofing from the soil particles, 

 thus enabling the surviving bacteria to obtain a greater food supply, 

 in consequence of which there is a greater availability of the organic 

 nutritive matter of the soil. 



