BY R. GREIG-SMITH. 8111 



the only agents which limited the multiplication of bacteria. 

 They did not directly test for toxins; and, although the reasons 

 which they bring forward* in support of the absence of toxins- 

 sound very convincing, yet a more intimate knowledge of the 

 behaviour of the toxins enables one to interpret their experimental 

 results generally in a manner different from what they have 

 done. The presence of toxin and the activity of its group- 

 specificity cannot be ignored. Furthermore, the identity of the 

 toxins, produced by superheating soils, with the toxins of untreated 

 soils has not as yet even been suggested, and certainly has not been 

 proved. The behaviour of the nitrifying bacteria towards this 

 toxin, which is one of Russell and Hutchinson's strongest ar»u- 

 ments against the presence of soil-toxins, cannot, therefore, l)e 

 considered. 



Toxin is undoubtedly present in soil, and although it may not, 

 in ordinary or natural circumstances, be absolutely toxic, yet it 

 is sufficiently active to make itself evident as a restrainer. The 

 soil-nutrients accelerate the growth of bacteria, the soil-bacterio- 

 toxins restrain their multiplication, and an equilibrium becomes 

 established. The phagocytes doubtless play a part, assisting the 

 toxins, and the agricere also assists in preventing the rapid 

 solubility of the nutrients. 



EXPERIMKNTAL. 



In the various experimental results that follow, Bac. prodigiosus 

 was used to indicate the growth or otherwise of bacteria. This 

 bacterium is easy to detect, it grows rapidly, and it belongs to 

 the class of putrefactive bacteria which are, presumably, the- 

 active agents in soil-decomposition. 



The soils were obtained from the Hawkesbury Agricultural 

 College, from an orchard near the summit of the Kurrajong, and' 

 from the garden around the Society's House. They were gener- 

 ally air-dried upon arrival in the laboratory, but in many cases, 

 this was unnecessary, and in certain cases the fresh soil was 

 used. 



*Journ. Agric. Sci. iii (2), 117-118. 



