H. B. Hutchinson and A. C. Thaysen 4o 



growth, of extracts of soils which have been treated with antiseptics is 

 attributed to an increase of nutrients consequent on such action. 



In a later paper the possible significance of toxins both labile and 

 stable, and of antitoxins is discussed. 



A further contribution to the subject was made by Bottomley(3) 

 who determined the growth of denitrifying and nitrogen-fixing bacteria 

 when carried into extracts of soil and of manure. It is stated that the 

 former bacteria thrive well whilst the latter do not. We have repeated 

 these experiments with soil but without being able to obtain any 

 corroborative results. 



Experiments somewhat similar to those of Greig Smith have been 

 carried out in India by C. M. Hutchinson (4). In connexion with the 

 results of various plate culture experiments he assumes without offering 

 any proof that the varying number of colonies on the different plates is 

 "due to the variation in the content of bacterio-toxin in the several 

 soil extracts from different treatment, so that plates showing large 

 numbers of colonies will result from extracts containing small quantities 

 of toxins and vice versa." He further assumes that these toxins are 

 destroyed by exposure of the soil to sunlight and air, as well as heat, 

 and also observes that toluene must have a similar effect since the want 

 of toxicity in toluened soil extracts cannot be due merely to redistri- 

 bution of toxin in the soil. It may be noted however that the latter 

 assumption difEers from that of Ureig Smith, who does not recognise 

 the destruction of toxins by volatile antiseptics. 



C. M. Hutchinson does not advance any experimental data in support 

 of these views, and in fact, in order to account for the somewhat con- 

 tradictory results it becomes necessary to set up fresh attributes of the 

 various soil extracts. It is stated, for instance, that heating of an extract 

 of fresh soil for 15 minutes is sufficient to produce toxins but not to 

 destroy them, while heating for 60 minutes both produces and destroys 

 them. In the case of the extract of air-dried soil, it is supposed that the 

 proportion between toxins and organic matter might be such that 

 15 minutes' heat destroys the toxins initially present and also such as 

 are formed by heating from the organic matter in the soil extract. 



These investigators have not only supposed that their results de- 

 monstrated the presence of toxins as normal constituents of the soil, 

 but they argue that the toxins are decomposable by some of the partial 

 sterilisation methods adopted in our investigations, and that therefore 

 the improvement in bacterial growth we observed in partially sterilised 

 soils is due simply to the destruction of toxins. This extension of the 



