CHAPTER VII. 



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 recep- 

 tion. It is essential that the tubes for this purpose 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, solu- 

 tion ; 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. 8), as those with wire handles are apt to break 



Fig. 8. 



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 them. 

 When dry they are to be plugged with raw cotton. The 



