10 



GENERAL BACTERIOLOGY 



EXERCISE 5. 



FILLING TEST-TUBES AND FLASKS WITH CULTURE 

 MEDIA. 



GENERAL DIRECTIONS. In filling tubes be careful not to allow 

 the media to touch the neck of the vessel as this will cause the 

 cotton to stick to the glass when the plugs are removed. Place 

 the culture fluid to be tubed in a funnel arranged with a delivery 

 tube and stopcock (Fig. 2), from which it can be 



run into sterile vessels. Test-tubes should contain _ _ 



6-10 cc. of medium (about 3 cm. deep). Flasks 

 are to be filled about three-fourths full. 



SPECIAL DIRECTIONS. Fill 15 test-tubes and 

 preserve remainder of bouillon in flasks. 



EXERCISE 6. STERILIZATION OF CULTURE 

 MEDIA. 



EXPLANATORY. To sterilize culture media steam 

 is used almost exclusively either as streaming FIG. 2. Appara- 

 steam or under pressure. The unconfined steam tubes* 

 is applied in an apparatus known as a steam ster- 

 ilizer. Of the various patterns the Arnold is perhaps the most 

 satisfactory. It is effective, economical in the use of gas, and 

 does not allow the escape of large quantities of steam into the 

 room as a large part is condensed to be reconverted into steam. 



A simple steam sterilizer is shown in 

 > Fig. 3, and for student use is very 

 convenient. The method of using 

 either form is identical. Always 

 have plenty of water present before 

 heating. Exposure is made on three 

 consecutive days for 20 minutes, be- 

 ginning to count time when the ma- 

 o terial reaches the temperature of the 



FIG. 3. Simple sterilizer consisting steam > which wil1 varv with different 



of a galvanized iron pail with a cover substances and the volume treated. 



a ana a raise bottom o. 



Between successive steamings culture 



media should be kept under conditions favorable to spore germi- 

 nation,' i. e. , at the room temperature. This method of steriliza- 

 tion is known as the discontinuous method or Tyndalization. 



For 'the employment of steam under pressure the autoclave is 

 essential. The lid should contain a thermometer as well as a 



