48 CLINICAL BACTERIOLOGY AND 



the result will be an even circular scratch, at which point, 

 when pressure is applied, the tubing will break, leaving 

 the two ends clean-cut. 



The proper length of tubing thus made should be taken 

 up and rotated by the right and left hand in the flame 

 of the blow lamp, the flame being in the middle of the 

 tubing. When it has become sufficiently plastic to move 

 about freely, it should be removed from the flame and 

 steadily drawn out until it reaches about 6 inches in 

 length. The middle of this tubing should now be allowed 

 to touch the flame, and with gentle traction the ends part, 

 leaving two capillary pipettes. 



Many failures will follow the operator's labours at the 



I 



Fig. 21. — A Simple Capillary Pipette. 



outset, but, as already stated, glass tubing is cheap, and 

 perseverance will bring its own reward. 



To reduce the risk of these failures, however, the follow- 

 ing points should be noted : 



The glass should be uniformly heated from start to finish, 

 and the rotation should be complete, failing which one side 

 would become more plastic than the other, and the resulting 

 capillary would be removed from the central axis of the 

 tube. 



Again, the flame throughout does not give off the same 

 amount of heat; therefore it is wise to move the tube up 

 and down in the flame, and also from side to side. Failing 

 this precaution, we shall find a bulb corresponding to the 

 centre of the flame, with capillary taperings on either side, 

 due to the fact that the greatest amount of heat is found 

 at the sides of the flame. 



