46 R. GREIG-SMITH. 



toxins were produced by micro-organisms, the growth of 

 which were favoured by certain plant secretions. 



Steaming the Soil. 

 Although Koch showed that steaming tiie soil cured soil- 

 sickness, and enabled plants to grow satisfactorily, the 

 beneficial effect of steam upon soil was well known to those 

 workers who used the pot method in experimenting with 

 the growth of plants. The reason for the effect, however, 

 appears to have been first sought by Kichter 1 in 1896. An 

 increase of the organic constituents soluble in water was 

 obtained, and he concluded that this was the cause of the 

 increased fertility. It was later shown that there was also 

 a liberation of the fixed constituents 2 and a greater avail- 

 ability of the nitrogen of the soil. 3 There is also a pro- 

 duction of poisonous substances which are irregular in their 

 action, some plants being decreased, while others are in- 

 creased. These toxins may be of an acid nature, for they 

 are put out of action by lime. 4 



In testing the respiration of a soil sterilised by steam, 

 and subsequently seeded with bacteria, Fischer 5 showed 

 that although the numbers increased as time went on, the 

 amount of carbon dioxide given off gradually fell away. 

 From this he argued that after a period of fermentative 

 activity, the bacteria became quiescent and although show- 

 ing an increase in numbers, they had a low fermentative 

 power. He did not consider that the increase in the 

 bacterial numbers resulted from an enhanced availability 

 of the soil constituents, but that it was due to the nutrients, 

 previously locked up in the bodies of the bacteria coming 

 into solution during sterilisation. The iucreased numbers, 



1 Richter through Fischer, Cent. Bakt. 2 te, 22, 671. 



2 Konig, Hasenbiiumer and Coppenrath, Ibid., 17, 261. 



3 Dietrich through Fischer, Ibid., 22, 671. 

 * Schultz, Ibid., 19, 341. 



6 Fischer, Cent. Bakt. 2 te, 22, 671. 



