430 



T. L. HILLS 



solution (Asliby's) were placed in each of ten liter Erlenmeyer 

 flasks. To each of these flasks 10 grams of soil were added and 

 the flasks and contents sterilized at 10 pounds for thirty min- 

 utes. After cooling each flask was inoculated with a suspension 

 of Azotohacter in sterile distilled water. Finally, one half of 

 the flasks were inoculated with 10 cc. of a suspension of 40 

 grams of normal soil in 400 cc. of sterile distilled water and the 

 remaining half were similarly treated using protozoa-free soil. 

 The flasks were incubated at 25°C. for three weeks. Previous 

 to determining the total nitrogen the flasks were examined in 

 order to ascertain whether or not protozoa were present. In 

 those flasks inoculated with soil containing the protozoa they 

 were present and in a very active state and in those inoculated 

 with soil free from protozoa they were not found. 



The results of the total nitrogen analyses are given below. 



TABLE 8 

 Rate of fixation of free nitrogen in solution with and without protozoa 



ANALYSES 



TREATMENT 



With protozoa. . . 

 With protozoa. . . 

 With protozoa. . . 

 With protozoa. . . 

 Without protozoa 

 Without protozoa 

 Without protozoa 

 Without protozoa 



TOTAL NITROGEN PER 100 CC. 

 OF SOLUTION 



After 21 days 



Average 



31.74 



33.79 



The results of the total nitrogen determinations revealed a 

 difference of 2.05 mgm. of nitrogen in favor of the cultures with- 

 out the protozoa. Apparently the protozoa had a slight detri- 

 mental effect on nitrogen fixation in solution. The protozoa- 

 free cultures contained 33.79 mgm. of nitrogen and the cultures 

 with protozoa contained 31.74 mgm. of nitrogen. 



Thus it appears that in hquid cultures where the protozoa 

 are in an actively motile state they seem to exert a harmful 



