Eight days after the elimination of diatoms, a thin-filamented blue-green algal bloom appeared in the cultures. This was temporarily checked by the addition of 20,000 uniits,l of penicillin G and 3,600 unit/l of streptomycin sulphate. Earlier experiments have shown that 40,00 units/l of each of each of these antibiotics provide effective bacterial control in static cultures without apparently harming either Acartia or Euplotes, although the Euplotes populations decline due to elimination of their bacterial food. The lower level of antibiotics used resulted in the disappearance of the blue-green after about 1week. Two months later , the same problem returned and was treated by adding both penicillin G and streptomycin sulfate at 40,000 units/l. There has been on further recurrence of blue-green algae. The effect of antibiotics upon the bacterial population is quite temporary , due to their rapid removal by foaming
The main purpose ot the continuous-culture device in this laboratory is to provide a constant and ready source of material for physiological and bioassay studies using a minimum effort to maintain stock cultures. Culture tanks themselves could be use as experimental vessels for population studies, and the number of such experimental vessels may be in-creased by proportionately adding foam towers in parallel arrangement. The present system satisfies our immediate needs and serves as a pilot plant for larger systems which will eventually provide food for larger filter-feeding species. When this is constructed, laboratory investigations including an entire food chain will be possible.