CHAPTER VI. 



Preparation of the tubes, flasks, etc., in which the media are to be 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 4 to 6 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 hav- 

 ing a reed handle (Fig. 18), as those with wire handles 



FIG. 18. 



Brush for cleaning test-tubes. 



are apt to break through the bottoms of the tubes. 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 



