June 12, 1916 Influence of Arsenic upon Soil Organisms 401 



obtained in the presence of arsenic where the soil extract was used. This 

 fact would seem to indicate that the main stimulation brought about by 

 arsenic is due to its action upon injurious species. The results obtained 

 in the presence of arsenic and absence of mannite indicate that the Azo- 

 tobacter can not use the arsenic as a source of energy. The small fixation 

 where the soil extract was used may be due to the nitrogen-fixing organ- 

 isms obtaining a small quantity of carbon compounds from algae which 

 may have grown in the complex flora. 



The results given in Table VII pointed strongly to the conclusion that 

 the stimulating influence of the arsenic was due in part to an indirect 

 action upon the nitrogen-fixing organisms, possibly an action which it 

 exerts upon the cellulose ferment. A series was therefore arranged in 

 which the cellulose ferments were used in connection with the Azoto- 

 bacter. 



In this series loo-gm. portions of the high humus soil (A) were placed 

 in covered tumblers and sterilized in the autoclave and then treated as 

 in Table IX. The Azotobacter was inoculated into 100 c. c. of Ashby 

 solution. After three days the solution was thoroughly shaken and 5 c. c. 

 of the solution were added to the sterile soil. The cellulose ferment was 

 added by making a suspension of the organism in sterile distilled water 

 and adding 5 c. c. of this to the soil. The moisture content was made up 

 to 1 8 per cent and incubated for 1 8 days. Six samples of each were used, 

 so that the results reported are the averages of six closely agreeing deter- 

 minations. The results are given in Table IX. The cellulose ferments 

 used were Bacillus rossicus, isolated by Kellerman, McBeth, and others 

 (1913) from Geneva (N. Y.) soils, and Pseudomonas efjusa, isolated by the 

 same investigators from the soils used in this work. 



Table IX. — Quantity of nitrogen (in milligrams) fixed in 100 gin. of soil with and 

 without arsenic in the presence and absence of cellulose ferments 



Treatment. 



Azotobacter chroococcum 



Azotobacter chroococcum, 0.0728 gm. lead arsenate 



Azotobacter chroococcum, Bacillus rossicus 



Azotobacter chroococcum, Bacillus rossicus, 0.0728 gm. of lead arsenate. . . . 



Azotobacter chroococcum, Pseudomonas effusa 



Azotobacter chroococcum, Pseudomonas effusa, 0.0728 gm. of lead arsenate . 



Azotobacter B 



Azotobacter B, 0.0728 gm. of lead arsenate 



Azotobacter B, Bacillus rossicus 



Azotobacter B, Bacillus rossicus, 0.0728 gm. of lead arsenate 



Azotobacter B, Pseudomonas effusa 



Azotobacter B, Pseudomonas effusa, 0.0728 gm. of lead arsenate 



In this series, as in the previous series in which A . chroococcum was used, 

 it did not fix as much nitrogen in the presence of arsenic as it did in the 

 absence of it. A. chroococcum fixes nearly twice the quantity in the 



