﻿IX, B, 4 



Barber: The Pipette Method 



315 



stage in such a position that the groove g (fig. 1) will be nearly- 

 opposite the center of the condenser. 



2. Smear the upper edges of the moist chamber thickly with 

 vaseline, and add enough water to cover the bottom and to 

 saturate the filter-paper lining. If the moist chamber has been 

 exposed to dust, it is well to flame it lightly before adding the 

 vaseline or water. 



3. Sterilize the cover glass, prepared as described above, over 

 a diffused heat. The flame of a gas stove or the top of the 

 chimney of a Welsbach light gives a suitable heat. Avoid 

 heating so much as to burn off the vaseline film. 



4. Place the cover on the moist chamber, and press it down 

 so as to seal it at the edges. Mark the upper surface as 

 shown in fig. 4, using India ink or a glass pencil.' 



5. With a platinum loop or, better, with a pipette bent at the 

 tip, place drops of sterile broth 

 on the underside of the cover, 



CD 



a 



o o o 





CD 



8 c> 







Fig. 4. Cover glass marked with cross lines 

 of India ink, and supplied with hanging 

 drops of sterile fluid, a, drop to which 

 the bacteria to be isolated are added. 



of somewhat the size and ar- 

 rangement shown in fig. 4. The 

 bacteria may be placed in drop 

 a. This end of the cover is 

 placed next to the open end of 

 the chamber. 



6. Place the chamber on the 

 stage of the microscope, and 

 focus with the low power on 

 the center of the free edge of 



the cover. The edge should be approximately at the center 

 of the field. Lower the objective within 2 or 3 millimeters of 

 the cover glass. It is well to protect the open end of the moist 

 chamber temporarily with a piece of moistened filter paper. 



7. Make the capillary pipette as follows: 



(a) Lower the flame of the microburner to a narrow blue 

 flame not over 2 millimeters high. The smallest flame that 

 will remain lighted should be used, and the working table should 

 be free from drafts of air. 



(6) In an ordinary Bunsen flame draw out one end of a 

 piece of glass tubing into a straight capillary about 0.5 

 millimeter in outside diameter. 



' Fine straight lines may be made by dipping a fine capillary tube or rod 

 into India ink or asphalt cement spread on a glass slide. The smeared 

 capillary is laid on top of the cover in the position desired, and is then re- 

 moved. India-ink lines have the advantage of being insoluble in inomersion 

 oil. 



