﻿IX. B, 4 Barber: The Pipette Method 335 



glass is used, little difficulty will be found in bending it into any- 

 desired form over a small flame. Then the partition p, which 

 fits into grooves at the side of the isolating chamber, is slipped 

 down into place, and the cover is put into place and sealed with 

 vaseline. An oxygen-absorbing reagent may be placed in the 

 compartment b and a wholly or partially anaerobic condition 

 attained. 



Such a device is unnecessary for ordinary work, and even the 

 moist paper protecting the open end can usually be dispensed 

 with. If the bottom of the chamber is well supplied with water 

 and the cover well sealed on, small droplets will remain on the 

 inner half of the chamber for hours, even when the end is 

 uncovered and the apparatus unprotected by a bell jar. By 

 taking very simple precautions, one can work in a very warm 

 and dry room. 



DANGER OF CONTAMINATION 



Danger of contamination is very small, less than when ordi- 

 nary plate cultures are used, as there is no strong current of 

 air entering the chamber. Droplets of broth remain sterile for 

 many hours with the end of the chamber open and unprotected. 

 In work where special precautions are to be taken, one may 

 protect the end of the chamber with moist filter paper or the 

 paper hood while the pipette is in place, and at other times keep 

 the chamber on a glass plate protected by a bell jar or crystal- 

 lizing dish. 



PREPARATION OF ORGANISMS FOR ISOLATION 



As stated above, no preliminary dilution of the organisms to 

 be isolated is necessary. The material may be taken from any 

 source, and the emulsion of organisms may be of any density. 

 The organisms to be isolated may be in the majority, or they may 

 be surrounded by thousands of other organisms of the same or 

 another species. A single red corpuscle may be easily isolated 

 from undiluted blood. In selection experiments, one may sep- 

 arate any aberrant organism from myriads of others of the same 

 sort. The only requirement is that the organism is recognizable 

 and large enough to be seen under an oil-immersion lens. Ani- 

 mals, unicellular algae, or spores of fungi may be removed from 

 a thick emulsion of bacteria, washed with the pipette, and isolated. 

 Bacteria may be separated from pus or other pathological 

 material. 



There is always the possibility that a nonmotile organism 

 may not be viable. One can often save the labor of making 

 a long series in search of a living organism by a short prelim- 



