E. H. Richards 



309 



due to a combination with Azotobacter. Beijerinck and Van Delden^ 

 found that certain species of Azotobacter chroococcum in combination 

 with other bacteria were able to fix nitrogen more readily than in pure 

 culture. One of the organisms tested symbiotically by these workers 

 was B. lactis aerogenes. Beijerinck, however, could only fix about 

 1 mgm. of nitrogen per gram of dextrose with his combinations of 

 A. chroococcum + B. lactis aerogenes. The crude cultures from the 

 horse faeces were three or four times as active, but this may be due to 

 the fact that calcium carbonate was added to these, while Beijerinck 

 apparently used none. 



By the kindness of Professor A. Harden the strain of B. lactis aero- 

 genes at the Lister Institute was compared with the pure culture of the 

 capsuled organisms. They were found to be identical as far as tested. 



Samples of horse faeces, treated in different ways, were incubated 

 in duplicate without air current, at 18° C for 14 days. 1 c.c. of dextrose 

 culture was used for the inoculations. 



Inoculation of Horse faeces. Series 1. 



Another sample of horse faeces incubated in a similar way for 

 30 days gave the following figures: 



Inoculation of Horse faeces. Series 2. 



Original total nitrogen (grams) 

 Final total nitrogen (grams) 



Difference 

 Per cent, of original total N. 



Raw faeces inoculated both with soil and with the mixed culture, 

 all fixed small amounts of nitrogen, but after sterilization in the auto- 

 clave at 120° C, the only samples showing significant fixation were 

 those inoculated with soil; these gave the greatest increase found in 



1 Centr.f. Baki. 2 Abt. Bd. ix, 1902, No. 1, p. 3. 

 Journ. of Agric. Sci. viii 21 



