730 CONTRIBUTIONS TO OUR KNOWLEDGE OP SOIL-FERTILITY, vii.-xi., 



The graph of these numbers is interesting, but the water-control 

 showed that distilled water had a destructive action upon the added 

 bacteria; and as this was not desired, tap-water was subsequently 

 employed. 



In the next experiment, the soil had been air-dried for two 

 days. 



Experiment iii. 



100 grams of dry garden-soil with tap-water. 



75 c.c. ... 

 100 c.c. ... 

 150 c.c. ... 

 200 c.c. ... 

 250 c.c. ... 

 Water-control 



1,000 bacteria became 



3 



115 



12 



12 



168 



1,093 



It is clear that the soil is toxic in all proportions used. In No. 2, 

 the plates showed that the culture was impure, and this suggested 

 that possibly extraneous bacteria might have an accelerating influ- 

 ence upon Bac. prodigiosus. This was tested in the following ex- 

 periment, which was made nine days later, the soil having been 

 stored for 11 days. In the second part, a drop of the unfiltered 

 extract of No. 1 was added to each test. 



Experiment iv. 



The soil furnished toxic extracts, although when compared with 

 Experiment iii., the toxicity appears to be diminishing. The pre- 

 sence of the mixed soil-bacteria did not materially influence the 

 growth of Bac. prodigiosus. Five days later, a further test of the 

 toxicity was made. 



