continuous culture on the Pratt medium with an organic matter (phenol or 

 glucose) used in the experiment. Then a continuous run was started with 

 the required dilution rate. When a steady state (constant concentration of 

 organic matter and constant number of bacteria) was reached, protozoa were 

 added to the reactor and the experiment was continued until a new steady 

 state was attained. Thus, the first part of the experiment (organic matter 

 + bacteria) served as a control for the second part (organic matter + 

 bacteria + protozoa). As for the protozoa, the infusoria ciliates 

 Paramecium caudatum , Ehrb. were used with the experiments with phenol, and 

 the zoof lagel lates Pleuromonas jaculans , Perty, in the experiments with 

 glucose. 



To clarify the interrelations of bacteria and protozoa in a medium de- 

 ficient in nutrients, experiments have also been performed with infusoria 

 ciliates P_. caudatum in Pratt solution in which the concentration of nit- 

 rate nitrogen was diminished to 1 mg/liter. All the experiments were con- 

 ducted at a temperature of 22 C. Altogether, the following experimental 

 variables have been used: 



1. Bacteria on complete Pratt medium with phenol at D = 0.02 hrs" 1 . 



2. Bacteria and infusoria on complete Pratt medium with phenol 

 at D = 0.02 hrs" 1 . 



3. Bacteria on complete Pratt medium with phenol at D = 0.04 

 hrs -1 . 



4. Bacteria and infusoria on complete Pratt medium with phenol 

 at D - 0.04 hrs" 1 . 



5. Bacteria on pratt medium given deficient nitrogen with phenol 

 at D - 0.02 hrs" 1 . 



6. Bacteria and infusoria on Pratt medium given deficient nitrogen 

 with phenol at D = 0.02 hrs" 1 . 



7. Bacteria on complete Pratt medium with glucose at D = 0.06 hrs" 1 . 



8. Bacteria and flagellates on complete Pratt medium with glucose 

 at D = 0.06 hrs -1 . 



9. Bacteria on complete Pratt medium with glucose at D = 0.08 hrs" 1 . 



10. Bacteria and flagellates on complete Pratt medium with glucose 

 at D = 0.08 hrs -1 . 



All the variables of the experiment were conducted with three replica- 

 tions. Every day the numbers of bacteria and flagellates were determined 

 in the reactor by direct counts in the Goryavev chamber at microscope magni- 

 fication of 900x for bacteria and 150x for flagellates. Infusoria were 

 counted in the Bogorov chamber under a MBS-1 microscope. To see the 

 balance of organic matter, the numbers of organisms were expressed in dry 



133 



