608 



T. J. MURRAY 



Mannite agar 



KjHP04 0.2 



MgS04 0.2 



NaCl 0.5 



Mannite 20.0 



H2O 1000.0 



Agar 15.0 



FeCU, 1 drop 10 per cent 

 Neutralized with KOH. 



Ashby agar 



K2HPO4 0.2 



MgS04 0.2 



NaCl 0.2 



CaS04 0.2 



CaCOs 5.0 



H2O 1000.0 



Agar 15.0 



Winogradski agav 

 K2HPO4.... 1.00 gram 



MgS04 3.00 grams 



NaCl 0.01 gram 



MnS04 0.01 gram 



CaCOa 10.00 grams 



FeCl3.2 drops 10 per cent 



H2O 1000 grams 



ir 15 grams 



The soil was plated and the plates were incubated at 30° C. 

 under aerobic and anaerobic (pyrogallic acid and caustic soda) 

 conditions for seven days and then counted. 



Experiment XI. Number of bacteria per gram on nitrogen-poor media. 



Aerobes 



Greater numbers of bacteria develop under aerobic than an- 

 aerobic conditions. There are more aerobic than anaerobic bac- 

 teria capable of growing on nitrogen-poor media. The number 

 of bacteria varies with the type of soil, the greatest number 

 being present in the greenhouse type and fewest in the clay. 



Two cultures of Azotobacter were picked from the aerobic 

 plates and two cultures were picked from the anaerobic plates. 

 These cultures were inoculated into 100 cc. of nitrogen poor 

 media, — Mannite solution, Winogradski solution and Ashby solu- 

 tion (same composition as the agars without the agar). The 

 two cultures taken from the anaerobic plates were kept, with 

 and without, oil. All inoculated material was incubated twenty- 

 one days at 30°C. 



