PIPETTES 33 



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 

 specimens. 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 



Fig. 14. — Pipettes. 



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. 



Under any circumstances both ends of the pipette must be sealed 

 up in a flame (the flame of a wax match will answer at a pinch), 

 and the tube labelled. 



Another variety of pipette which was much used for the collec- 

 tion of blood for the purpose of testing the serum reaction for 

 typhoid fever, is drawn out to a point at one end only, the other 

 being left wide and separated from the bulb by a constriction 

 (Fig. 14, b). The Open end should be loosely plugged with 

 cotton-wool, and serves as a mouthpiece. The manufacture of 

 these pipettes presents a little difficulty, but a small amount of 

 practice will enable the practitioner to turn out a perfectly 

 serviceable one on occasion. 



Wright's blood capsules (Fig. 15) are the best contrivances for 

 collecting blood when the serum has to be examined, and have 

 quite replaced the pipettes described above. They can be pre- 



3 



