PLUGGING THE TUBES AND FLASKS 



EXERCISE II 



PLUGGING THE TUBES AND FLASKS AND STERILIZING 

 THE GLASSWARE 



6. After the tubes and flasks are cleaned they must be 

 plugged. The plugged tubes and flasks and the Petri dishes, 

 all of which are to be used for holding culture media or in 

 making cultures, must be sterilized before they can be used. 

 The plugs should be neatly made and of the proper length and 

 firmness. The best quality^ of absorbent cotton is ordinarily 

 used for this purpose, although common cotton is employed in 

 some laboratories. If the latter is used, it should be first heated 

 to a very slight browning in the hot-air sterilizer. This drives 

 off the oil and kills the sporeS which it might contain. Glass- 

 ware is sterilized with dry steam or by means of dry heat, i.e. 

 in the hot-air sterilizer. (See method for sterilizing apparatus 

 and instruments in text-books.) 



7. Work for this Exercise. — Plug all of the tubes and flasks 

 with absorbent cotton and sterilize them, together with the 

 Petri dishes, in the hot-air sterilizer. After they are sterilized, 

 store them in the locker until they are needed. The Petri 

 dishes must not be opened until they are used. 



8. Plugging the Tubes and Flasks. — For this purpose 

 absorbent cotton is used. The rolls of absorbent cotton are cut 

 in short segments of from 5 to 7 cm. in length. A piece of 

 this narrow strip of sufficient length to give cotton enough for 

 the plug is torn off. The quantity varies, of course, with the 

 size of the mouth of the tube or flask, but a little experience 

 will enable one to estimate the quantity quite accurately. The 

 edges of the piece of cotton torn off are turned in and it 

 is rolled up to form a firm plug which should snugly fit the neck 

 of the tube or flask. It should be inserted into the tube for 

 about 2 cm. and the end should be nearly flat and smooth. 



