352 THE BIOLOGY OF STENTOR 



mented species like roeseli. A thick slide is easier to pick off the 

 microscope stage than the common thin ones. I use a depression 

 slide turned upside down. 



With a micropipette an animal is then transferred with minimum 

 fluid to the center of the drop of methyl cellulose. The stentor 

 must not be allowed to wander to the surface, for then, oddly- 

 enough, the ectoplasm will adhere and tear off when the animal 

 is moved. With an eyelash fastened to a narrow handle the animal 

 is then pushed to the bottom of the drop ; reason : a glass needle 

 is too sharp and may impale the specimen. 



The glass needle is then taken in hand and after gently moving 

 the stentor into position the proper cut is made. With practice the 

 needle can be precisely ''located" under the microscope so that 

 in time breakage becomes infrequent. After cutting at high magnifi- 

 cation, the objectives are shifted to low power and the specimen 

 removed with the micropipette and placed in a block cell with 

 several drops of filtered culture medium to wash off the methyl 

 cellulose. Washed specimens are then transferred to two large 

 drops of filtered medium in a shallow depression slide, the code 

 number of the experiment can be written in pencil on the frosted 

 edge, and the slide stacked '' pig-stye fashion " in a moist chamber. 

 For the latter I use plastic sandwich boxes, the bottoms of which 

 are covered with a thick layer of wet filter paper. One box will 

 accommodate about 2 dozen stacked slides. (Fig. 97c). At intervals 

 depending on the experiment, the slides are removed from the 

 chamber and examined by reflected light under the microscope, 

 moving them always in the same order, stacking them then in 

 reversed order in another moist chamber. When necessary, the 

 specimen can be transferred briefly to a drop of the methyl cellu- 

 lose for close examination under high magnification, rolling it into 

 position with the eyelash. On termination of an experiment, the 

 drop is shaken off the slide, leaving some moisture by which it may 

 be rubbed clean and dry with cheese cloth, and the code number 

 erased. I do not use elaborate cleansing methods because these are 

 unnecessary when control of bacterial flora is not involved. 



My experience agrees with the pioneer observations of Gruber, 

 that healing of cut surfaces is always prompt and effective. Even 

 if most of the ectoplasm is removed, the remainder will stretch 

 and manage to cover all the endoplasm (see Fig. 25c). Defective 



