﻿IX, B. 4 



Barber: The Pipette Method 



327 







or registered according to its position (fig. 8). As many as 

 from 50 to 60 drops may be placed on the same large cover. 



Each organism as it is isolated is placed in a small droplet 

 close to any one of these larger drops c (fig. 8), using the same 

 pipette for all. When the series is finished and the small drops 

 are examined to make sure that each contains but one organism, 

 each small drop of a pair is made to fuse with the larger one. 

 This may be done in several ways: (1) By means of a fresh 

 pipette filled with sterile broth, fluid is added to the larger 

 drop and the pipette withdrawn before the liquid spreads to 

 the smaller. Or the smaller drop may be enlarged to meet 

 the larger and the organism washed in. One may fuse all the 

 pairs of the series with the same pipette. (2) If agar or a 

 similar solid medium is used, one may pierce the large drop 

 with a coarse pipette and, by moving the mechanical stage, 

 slip the mass slightly until it meets the organism. This may 

 also be done with a bent plati- 

 num wire without the aid of 

 the microscope. (3) When the 

 small droplet is very close to 

 the large one, one may often 

 fuse the two by adding water 

 to the bottom of the isolating 



chamber sufficiently warm to Fig. S. a cover gUss with droplets arranged 



cause enough condensed mois- ^°' ^^ t"'""^"'^ ^f "^ °* isolations, c, a 



_ ° droplet shown on a larger scale with a small 



ture to join the drops. bacterium-containing droplet beside it. 



The organism may be placed directly on the surface of the 

 agar or gelatin, but the outlines of the droplet are less distinct 

 and it is then more difficult to make sure that the droplet contains 

 but a single organism. A drop of agar or gelatin may be placed 

 near the center of a large cover, the organism placed on it, 

 and a small cover pressed down on the organism. One may 

 then observe the growth taking place between the two covers. 



The moist chamber to which the cover is transferred should 

 be as shallow as the size of the droplets will permit, so that 

 there will be little air for the absorption of moisture from the 

 cover. A form convenient for large cover glasses may be made 

 by cementing strips of glass to a large slide. Immediately 

 before transferring to the cover, it is well to increase the mois- 

 ture on the cover slightly by placing warm water in the bottom 

 of the isolating chamber, and it is advisable to add condensed 

 moisture in the culture chamber by breathing on the bottom 

 of it. Unless the number of inoculated drops on the cover is 

 large, there should be extra drops of broth placed on it to 



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