PARAMOECIUM POSSESSING EXTRA VACUOLES 289 



to the jar when not in use (3). In following the offspring of a 

 single individual for several generations each of the daughter 

 cells was isolated in a watch glass and as fast as the individuals 

 divided a record was made of the number of vacuoles in each 

 and they were agam separated. The Syracuse watch glasses 

 that were used were sterilized in boiling water to which a little 

 clean paraffin had been added. This deposited an invisible coat- 

 ing on the glass which was, however, sufficient to prevent the 

 drop of hay infusion from spreading over the surface as it would 

 on perfectly clean glass. On the paraffined surface the fluid 

 rounds up and presents the minimum surface for evaporation (3). 

 It was found that the most satisfactory pipette for this work 

 had a short tip of almost hairlike fineness. The method of 

 making these has been described (3). 



It is rather difficult to find a method of slowing down the 

 animals for the purpose of making accurate observations with- 

 out killing them. The first method used was to place an indi- 

 vidual in a small drop of water and over this a cover glass was 

 lowered with the aid of a fine pan- of forceps. The cover had a 

 drop of hardened balsam at two corners which had been filed 

 down to the proper thickness and which prevented it from 

 crushing the animal. The excess fluid was drawn off with a piece 

 of filter paper. To recover the animal the slide was tilted 

 over a watch glass and by means of a stream of hay infusion 

 the cover and whatever was under it were flushed into the 

 crystal. This method was very laborious and slow, and the 

 chances of losing the paramoecium gTeat. The following method 

 has proved to be the better: An individual is placed on a slide 

 in a fairly large drop of the medium. The liquid is drawn off 

 with a pipette under the dissecting microscope, the animal being 

 kept as nearly as possible in the center of the drop. Finally, 

 enough of the fluid is removed so that the adhesion of the sur- 

 face film to the shde exerts sufficient pull to hold the animal 

 quiet. In the center of the drop the pressure is least and it sel- 

 dom causes a paramoecium to burst. Toward the edges, however, 

 the chances are very great that the animal will succumb almost 

 instantly to the greater pressure. In such a preparation the 



