82 CLINICAL BACTERIOLOGY AND HjEMATOLOGY 



piece of glass tubing about as thick as a lead-pencil and 

 about 4 inches long. This is done by holding the tube between 

 the finger and thumb at each end and softening it thoroughly in a 

 blowpipe or Bunsen flame, rolling it round and round the while. 

 When the central inch or more is quite plastic, the tube is removed 

 from the flame and the two ends drawn slowly apart with a steady, 

 uniform pull, and held apart until the glass is quite set. If this is 

 quite successful, the softened portion should be pulled out into a 

 tube about as wide as a steel knitting-needle, fairly uniform in 

 diameter, and if possible 2 feet long : this will make two pipettes 

 each a foot long. To separate them, melt the central portion in a 

 very small flame (such as that of a wax vesta), and pull them 

 apart rather quickly. If the capillary portion of your tube is 

 much less than 2 feet long it will only serve for one pipette, and 

 the place where it is melted must be close to one end. In either 

 case the result should be a pipette like that in Fig. 36. 



The most important part of the pipette is the tip, which is 

 represented, magnified three or four times, below the pipette. It 

 must narrow somewhat suddenly into a very fine capillary tube about 

 \ inch long, so as to oppose a considerable amount of friction to 

 the movement of a column of fluid in the tube. If the point is a 

 good one, you will have absolute control over the column, and 

 will be able to suck it up to a given point by means of the india- 

 rubber nipple with absolute precision. If the capillary tip is too 

 narrow or too wide, draw it out again until you have one that is 

 entirely satisfactory. 



This is now graduated into equal parts in the simple and 

 accurate method invented by Wright. Take a few drops of 

 mercury in a short test-tube, and cover it with a little water. 

 Put a mark with a grease pencil or with pen and ink on the 

 pipette about i inch from the tip : this is for the unit. Then 

 take the nipple between the thumb and finger of the right hand, 

 squeeze it, insert the tip in the mercury, and suck up the latter 

 exactly to the mark. Then withdraw the tip from the mercury 

 into the water and suck that up to the mark ; the mercury will 

 rise in front of it. When this is done, replunge the tip into the 

 mercury and suck up a second column. Repeat this process until 

 you have filled the tube with alternate layers of mercury and water, 

 each of exactly the same bulk (Fig. 27). When this is done, 

 remove the tube from the fluid and place it flat down on the table 

 still keeping sufficient pressure on the nipple to retain the fluids 



