50 CLINICAL BACTERIOLOGY AND 



satisfactorily one requires to exercise great care, and the 

 beginner is well advised to practise on empty test-tubes 

 first. Take a test-tube and rotate in a small flame first, 

 and, when thoroughly hot, rotation should go on in a full 

 flame until the sides of the glass begin to fall in. It 

 should now be drawn out into a narrow stem, and as soon 

 as it has become cool it is reheated in a smaller flame, 

 drawn out into a thin capillary stem, which is broken off, 

 set aside again to cool, and the point sealed in a very small 

 jet, candle flame, or by a wax vesta. 



When one is dealing with a fluid-containing test-tube, 

 greater skill and care is required. In the first place, the 

 operator must make sure the glass at the point the flame 

 touches is absolutely dry by careful heating. Then the 

 flame must not come too near the fluid, or it will boil and 

 crack the glass, and probably injure at the same time the 



Fig. 23. — Drawn-Out and sealed Test-Tube. 



chemical qualities of the fluid. This can be prevented, of 

 course, by holding the test-tube, while being heated in the 

 flame, at a proper angle, and not heating the tube too near 

 the surface of the fluid. Of course, if the flame is applied 

 too near the proximal end of the tube, the glass becomes so 

 hot as to scorch one's fingers. 



When there is an excess of the fluid in the tube neces- 

 sitating this condition, it is wise to heat the mouth of the 

 tube to red heat, holding the base by the left hand and by 

 a piece of glass tubing in the right hand, held also in the 

 flame until it becomes quite hot. Now fix the tubing to 

 the rim of the test-tube, first at one point and then at the 

 diagonally opposed point, and draw the whole into a 

 naiTOW stem. When cool, put the stem in the flame and 

 draw the two ends apart, sealing up the remaining opening 

 in the stem by applying a small flame to it. 



