CHAPTEE VI. 



Preparation of the tubes, flasks, etc., in which the media are to he pre- 

 served. 



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 possible to make them. For this purpose it is 

 advisable that both new tubes and those which have 

 previously been used should be boiled for some time, 

 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 having a reed handle (Fig. 21), as those with wire 



Fig. 21. 



Brush for cleaniug test-tuhes. 



handles are apt to break through the bottoms of the 

 tubes. All traces of adherent material should be care- 

 fully removed. When the tubes are quite clean they 

 may be rinsed in a warm solution of commercial hydro- 

 chloric acid of the strength of about 1 per cent. This 

 is to remove the alkali. They are then to be thor- 

 oughly rinsed in clear, running water, and stood top 

 down until the water has drained from them. When 



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