TECHNIQUES 34I 



transferred to a caster dish or other shallow container and examined 

 for stentors under low powers of a stereomicroscope. If stentors 

 are found, the whole sample container may then be rotated for 

 gentle agitation and more samples poured out. A portion of the 

 original sample is then passed through filter paper of medium 

 porosity which will remove all large forms and pass only minute 

 organisms on which stentors can feed, and this natural medium 

 can then serve for the starting of cultures. 



If stentors cannot be collected in the field they may be obtained 

 in mixed culture from several biological supply companies. 



The next step is to select stentors out of the sample dishes, 

 leaving competitors and predators behind. For this purpose micro- 

 pipettes are necessary and the ones I use are made from narrow, 

 polyethylene, catheter tubing obtainable from surgical supply 

 companies. This and other items of culture technique are illustrated 

 in Fig. 96. The tubing is softened by placing it across the narrow 

 flame of a wing-top gas burner and pulled out to a fine point. The 

 degree of heating is critical. If too cool the tubing breaks when 

 pulled and if too hot it collapses. One can expect to spoil a dozen 

 pipettes before one gets the knack. When good tubes are drawn they 



A. To the right: micropipette (actual size) with poly- 

 ethylene tip, rubber tubing "bulb", and glass rod plug; as well 

 as fine wire (bent) used when cleaning. To left: drawing out 

 polyethylene catheter tubing over wing-top burner for pipette 



tips. 



B. Glass block cell containing i ml in which all specimens are 



clearly visible. 



C. Culture in jar with hole punched in cap, examined briefly 

 with spotlight and magnifying glass to follow development of a 



culture. 



D. Development of clones. Single stentor first introduced 

 into one cell of deep depression slide; transferred to test tube 

 when multiplied to about 25 animals; transferred again from 

 hundreds in the test-tube to a cotton-plugged Ehrlenmeyer 

 flask. Filtered culture medium plus culture of food organisms 



used throughout. 



E. Migration tube for obtaining clean stentors. Main body 

 of half-inch diameter tube is covered with black plastic 

 electrician's tape and filled with clean water. Concentrated 

 S. coeruleus introduced at {x) will migrate away from lighted end 



and are recovered, clean, at other end {y). 



