﻿IX, B, 4 Barber: The Pipette Method 333 



rather thick capillary is drawn out into a hair point, d (fig. 6) , 

 and the end cut off, as described in the technique of making ordi- 

 nary pipettes. Only the hair point is turned up. This can 

 usually be done by simply holding it above the flame of the 

 microbumer. The upward draft of hot air softens the glass 

 and bends it vertically. This pipette is supplied with liquid; 

 the organism is taken up and washed well back as described for 

 the ordinary inoculation pipette. Then the hair point is broken 

 off, and one has a straight, very sharp-pointed needle with the 

 dose back of the tip and enough liquid present to wash it out. 

 Such pipettes with the contained dose may be sealed at the tip 

 and kept until a convenient time for inoculation. This modifi- 

 cation has been used in the inoculation of doses of Bacillus tuber- 

 culosis consisting of one or few bacilli.^^ If desired, the dose 

 may be discharged into the needle of a syringe and inoculated 

 in that way. The pipette is gradually withdrawn from the 

 needle as the dose is discharged into it. Semifluid agar or other 

 substance may be placed in the syringe and in the base of the 

 needle in order to carry out the dose. In most cases it is unnec- 

 essary to use the syringe. The technique of inoculation into 

 living cells will be described below. 



DETAILED DESCRIPTION OF CERTAIN STEPS IN THE ISOLATION 



METHODS 



MOISTURE 



The necessity of keeping the proper amount of moisture in the 

 isolating chamber cannot be overemphasized. Drying or over 

 concentration of the medium is fatal to some organisms, besides 

 increasing the difficulty of isolation. The index of the proper 

 amount of moisture is the presence on the cover of very small 

 droplets of condensed moisture, the film resembling fine stip- 

 pling (photomicrograph, Plate I, fig. 1). This stippling of con- 

 densed moisture also aids the eye materially in locating the 

 edge of droplets. Much depends on a proper amount of vaseline 

 on the cover (see page 314). If large droplets of condensed 

 moisture are formed, it becomes difficult to make the small 

 droplets necessary for isolation. In this case one usually finds 

 a suitable area in the neighborhood of a large hanging drop. 

 One can usually supply the necessary film of moisture by placing 

 slightly warmed water in the bottom of the isolating chamber. 

 Distilled water may be kept conveniently at hand in a small 

 reagent bottle closed with an ordinary medicine dropper. The 



'Woum. Med. Research (1909), 20, 1. 



