34 CLINICAL BACTERIOLOGY AND HEMATOLOGY 



which is drawn out into a narrow tube at least 6 inches long, 

 tapering gradually to the extremities (Fig. 14, a). To make such 

 a pipette, take a piece of glass tubing about 6 inches long and a 

 I inch wide, and heat it in a luminous gas flame at a point ^ inch 

 or so from the centre. Continue the heat until the _ glass is 

 thoroughly softened over at least J inch of its length, turning 

 the tube round all the time ; then remove it from the flame and 

 draw the two ends apart with a steady, uniform pull, so that the 

 heated portion draws out into a capillary tube several inches in 

 length. Repeat the process at a point about i inch from the 

 tapering end of the larger portion of the tube ; heat the bulb, and 

 then seal off both ends of the capillary portion before the bulb 

 cools. 



The pipettes are necessarily sterile, having been drawn out of 

 partially melted glass, and they will remain sterile indefinitely. 



Fig. 14. — Pipettes. 



Of course, the exterior of the glass will become contaminated, 

 and it should be passed through the flame before use. 



The ends of the tube being sealed up while the bulb contains 

 heated air, it follows that the bulb will contain a partial vacuum 

 on cooling. This fact is made use of in the collection of speci- 

 mens. Suppose, for instance, we wish to take some blood from 

 a heart at a post-mortem examination for investigation at a 

 distance. A point on the surface of the heart is first seared with 

 a hot iron to destroy any germs which might be present, and the 

 end of the pipette (still sealed) is thrust through into one of the 

 cavities. It is then broken off by dexterous pressure against the 

 heart wall, and the pipette will fill slowly with the blood. Another 

 method is to break off the tip of the pipette and to warm the bulb 

 before making the puncture. The fluid will rise as the bulb cools ; 

 or both ends may be broken up and the fluid drawn into the bulb 

 by gentle suction. 



