CHAPTER VI. 



Preparation of the Tubes, Flasks, etc., in which the Media are to be 

 Preserved. 



While the media are in course of preparation it is well 

 to get the test-tubes and flasks ready for their reception, 

 and it is essential that they should be as clean as it is pos- 

 sible to make them. For this purpose it is advisable that 

 both new tubes and those which have previously been used 

 should be boiled for about thirty to forty-five minutes in 

 a 2 to 3 per cent, solution of common soda ; it is not necessary 

 to be exact as to strength, but it should not be weaker than 

 this. At the end of this time they are to be carefully swabbed 

 out with a cylindrical bristle brush, preferably one with a 

 reed handle (Fig. 21, a), as those with wire handles are apt 

 to break through the bottoms of the tubes, though Messrs. 

 Lentz & Sons, of Philadelphia, have in large part eliminated 

 this objection from the wire-handle brush depicted in Fig. 

 21, b. All traces of adherent material should be carefully 

 removed. When the tubes are quite clean they may be 

 rinsed in a warm solution of commercial hydrochloric acid 

 of the strength of about 1 per cent. This is to remove the 

 alkali. They are then to be thoroughly rinsed in clear, 

 running water, and stood top down until the water has 

 drained from them. When dry they are to be plugged with 

 raw cotton; this requires a little practice before it can be 

 properly done. The cotton should be introduced into the 

 mouths of the tubes in such a way that no cracks or creases 



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