PREPARATION OF CULTURE MEDIA 25 



survive, they will develop during the next 24 hours, and 

 the third exposure to steam will complete the sterilization. 

 The apparatus used for this purpose is the "Arnold Steam 

 Sterilizer." The usual form used is seen in Figs. 13 and 

 14. Fig. 13 illustrates the appearance of the ordi- 

 nary form with the hood off. Fig. 14 shows the inside 

 arrangement, a and b being two compartments connected 

 by small holes, and in which a certain amount of water 

 has to be kept. The water contained in the inner com- 

 partment (a) is brought to a boil by a Eunsen burner, 

 the steam rising through a number of holes in the bottom 

 (c) into the chamber (d). The steam condenses at the 

 top of the chamber and returns between two sheet-copper 

 walls (e, e) to the large compartment (b). A larger form 

 of steam sterilizer, constructed on the same principle, is 

 convenient for sterilizing large amounts of the media. 



EXERCISE IV. PREPARATION OF PEPTONE-BROTH (FRENCH : 

 BOUILLON) AND DUNHAM'S PEPTONE-SOLUTION 



1 . Weigh the saucepan and measure 600 c.c. of tap- 

 water into it and heat. 



2. Dissolve, when hot (but not boiling), 6 g. of pep- 

 tone. 



3. When completely dissolved, replace the evapo- 

 rated water and divide into two equal amounts (300 c.c. 

 each). 



4. Filter one part twice through the same filter 

 (paper) and distribute into twenty-five tubes. Sterilize 

 in autoclav for 5 minutes at 120. This is Dunham's 

 peptone-solution. 



5. Dissolve completely i g. of extract of beef in the 

 other 300 c.c. 



