40 
7. Make one microscopic preparation from the agar and stain the organ- 
sims with methylene blue. Draw and describe the organisms as seen with the 
oil-immersion objective. 
8. The relative number of these organisms is soils A and B can be judged by 
the rate and extent of the development of the brown film. 
(a) What is the shape of the Azotobacter^. 
(b) Is the organism motile? 
(c) How does it compare in size with other bacteria? 
( d ) What organisms have you studied of which it reminds you? 
(e) Is the organism aerobic or anaerobic? 
(0 What is the value of Azotobacter to the soil? 
(g) Where did the nitrogen come from that is in the film on the 
liquid in the bottles? 
(h ) What use does Azotobacter make of the mannite? 
(0 What purpose is served by the calcium carbonate? 
