﻿IX, B. 4 



Barber: The Pipette Method 



339 



chamber, supplied with a cover, is placed on the stage. The 

 pipette is then turned point upward and adjusted so that it 

 may enter the chamber. The tip is focused under the low power, 

 and the organism is discharged into a hanging drop on the 

 surface of the cover. It may then be washed free from bacteria 

 or other organism if desired ; it may be grown on the cover or 

 transferred to a watch glass, a test tube, or other receptacle. 



The low powers of the microscope are most convenient for 

 this work, but a ^ objective may be used for smaller organisms. 

 In this case, a flat piece of cork is perforated with an opening 

 about 1 centimeter in diameter and the opening is enlarged funnel 

 Iwise on one side so as to admit the objective. A cover glass 

 is sealed with vaseline to the other side of the cork, and the 

 float is placed cover side down on the water. One may adjust 



Fig. 13. A special pipette in position for isolating organisms from the bottom of a Petri dish. 

 p and pa, metal plates screwed to the stage for the attachment of the pipette holder. The 

 complete pipette holder is used, but only a portion of it is shown in the figure. 



a pipette under the float and focus the higher power of the 

 microscope on the tip and the liquid surrounding it. If it is 

 desired to select organisms deeper in the liquid with the high 

 power, a short, thick rubber tube or hollowed rubber stopper 

 is placed around the base of the lens and the free margin smeared 

 with vaseline. A large cover is placed on a dry slide, and the 

 objective with the rubber tube is lowered to the cover. The 

 smeared edge reaches the cover and seals fast to it, and the 

 lens is made to descend until one can focus below the cover. 

 Any stained object on the slide will facilitate the focusing. On 

 raising the objective, the cover comes up with it; then it may be 

 lowered into the water containing the organisms to be isolated. 

 If organisms cling to the cover on bringing out the objective, 

 they may be picked off from the cover with the pipette, or 

 the pipette may be adjusted and isolation carried out as in the 

 case of the cork float. 



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