BY R. GREIG-SMITH. 



822a 



The Action of Toxin on Soil-Bacteria. 



So far, the experimental results have been obtained with 

 Bac. prodigiosus, a bacterium taken for several reasons, the chief 

 being that it is a putrefactive microbe, and it can be easily- 

 grown and detected. But the data obtained with it also apply 

 to other soil-bacteria, although the effects are not so marked. 

 The soil-bacteria appear to be more or less immune, for we cannot 

 believe that the soil-toxin is specific for so rare a soil-organism 

 as Bac. prodigiosus. In counting soil-bacteria, one has to prepare 

 extreme dilutions, because, in the plates containing strong dilu- 

 tions, bacteria such as Bac. Jluoreseens will prevent the growth 

 ■of other soil-bacteria. 



In the following experiments the extracts were made with 

 tO'5 % NaCl and portions of the filtered extracts were seeded 

 with portions of the untiltered suspensions. After one day's 

 incubation, the dilutions were prepared. The plates were incu- 

 bated, in the first case for 1, 2, and 3 days; in the second case, 



for 2 days- 

 Experiment xii. Kurrajong Soil. 



At start 



After incubation 

 for I day. 



Extract 



Extract boiled.. 

 Saline (control) 



Colonies. 



100 



20,700 

 156,400 

 133,000 



Approximate Percentage Analysis. 



Bac. flao- 

 re'icen'i. 



-3 



3 



4 



27 



r , fcsmall colo- 



Large sua- \ ■ , „ 

 , -P- ,., nies of B. 



colonies. 



63 



1 

 I 



10 



biyeminus 

 major. 



90 

 90 

 60 



Other 

 colonies. 



39 



5 



6 

 3 



