344 THE BIOLOGY OF STENTOR 



tinued source of food organisms will of course have been retained 

 in the film adhering to the emptied jar. It is well to have three or 

 four jars of the same stock. These can be developed by splitting 

 the contents of one jar between two and refilling both to the top 

 with filtered lake water, adding more cotton as needed. 



These procedures may not appear elegant but they have served 

 to maintain healthy stock animals in more than sufficient abundance 

 for my micrurgical operations continuously for 8 years, during 

 which not one of lo stocks has died out. The same method has 

 been used successfully for growing coeruleus, polymorphtis, roeseli, 

 and introversus. For the last named, skimmed milk must be added 

 very sparingly and never when clouds of uneaten colorless flagel- 

 lates are still present. In my experience, the cultivation of other 

 species like niger and multiformis is attended with great difficulties 

 and probably calls for exploring distinctly different methods. 



Temperature at which the stentors are grown is another 

 important factor. Schwartz found that stentors do better at lower 

 temperature than at higher (io° vs. 22°C). I have found that in 

 winter the culture room must be thermostatically controlled 

 to avoid wide changes in temperature. 



Genetically more uniform material is assured by developing 

 clones or cultures derived from a single individual. This is best 

 done after a good culture of the wild stock is obtained, for one can 

 then use filtered water from the culture itself as a starting medium 

 and be sure of its optimal nature. First one should develop a 

 separate culture of food organisms, either by nutrifying coarse- 

 filtered Stentor culture fluid with skimmed milk or by growing 

 any of the food organisms soon to be listed. Into a deep depression 

 sUde holding about i ml is isolated one stentor in a small drop, 

 checking at once that only a single animal is present. Then are 

 added 5 drops of the filtered parent culture and 5 drops of food 

 organisms. The slide is placed in a moist chamber and more food 

 organisms can be added as needed. One should of course start with 

 several such isolations to assure that at least one will be successful. 

 Further addition of food culture may be necessary. When about 

 25 stentors have developed, the contents of the slide are transferred 

 to a 25 ml test-tube with aluminium cap into which have previously 

 been added, at the bottom, 10 ml of food organisms and, on the 

 top, the same amount of filtered parent culture medium. When the 



