﻿IX, B, 4 Barber: The Pipette Method 347 



I have used this apparatus in some experiments with mixtures 

 of cholera vibrios and Bacillus pyocyaneus. A pipette charged 

 with a dilution of cholera agglutinating serum will attract only 

 B. pyocyaneus, while a pipette supplied with B. pyocyaneus ag- 

 glutinating serum will furnish pure cultures of cholera from the 

 same mixture, even though B. pyocyaneus has so far over- 

 grown the other that the cholera can no longer be detected by 

 the plate method. If the bacteria are not in pure culture in 

 the pipette, one or the other species may be so far in the majority 

 that it is easy to separate them by the plate method. The experi- 

 ments with cholera mixed with other bacteria are as yet un- 

 finished, but the technique is far enough developed to justify a 

 brief preliminary description here. There are many variations 

 possible in this technique, some of which will be described in a 

 subsequent article. 



The flask, shown in fig. 16, is a very convenient holder for 

 pipettes temporarily removed from the pipette holder. The tip 

 of the pipette is left just above the surface of the liquid, so that 

 it will remain moist. Agglutinating serums, stains, or other 

 fluids may be kept for days in this way, ready for use at any time. 



INOCULATION INTO LIVING CELLS" 



The technique of inoculation of microorganisms, stains, fix- 

 atives, or other substances into the protoplasm or vacuoles of 

 living cells is subject to some requirements not found in the 

 simple isolation of cells. The tip of the pipette must be of such 

 a fineness as to minimize the injury to the cells inoculated and 

 of sufficient rigidity to pierce the cell wall. An injection force 

 has to be employed suflSciently great to overcome cell pressure, 

 capillarity in the very fine tip, and any obstruction in it. A 

 pipette point, such as is shown in a, fig. 19, will meet the first 

 requirements, and the necessary force for injection is obtained 

 by the expansion of mercury. The isolating chamber, pipette 

 holder, and microburner are the same as those described under 

 method I. 



The special pipettes may be made of the same sort of tubing 

 as for isolating pipettes, although glass with a slightly thicker 

 wall (about 0.7 millimeter in thickness) is preferable. Either 

 hard or soft glass, if tough and of good quality, may be used. 

 A piece of tubing about 35 centimeters in length is bent at one 

 end into the form shown in fig. 17. The distance from the top 

 to the bottom of the curved portion should be about 5 centimeters. 



" First described in Journ. Infect. Dis. (1911), 8, 348. 



