CHAPTEE 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 strong solution 

 of common soda, about a 4 or 6 per cent, solution ; it 

 is not necessary to be exact as to the strength, but it 

 should not be weaker than this. At the end of this 

 time they are to be carefully swabbed out with a cylin- 

 drical bristle brush, preferably one having a reed handle 

 Fig. 18), as those with wire handles are apt to break 



Fio. 18. 



Brush for cleaning test-tubes. 



through the bottoms of the tubes. All trace 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 



