BACTERIOLOGICAL TECHNIC 21 



pah. It is advisable to add about 200 c.c. of water to 

 this to allow for evaporation. 



3. Cut and shred 15 grams of agar, add this to the 

 water, bring to the boiling point, and keep at this 

 temperature until the agar is completely dissolved. 

 Violent boiling should be avoided and the mixture 

 should be stirred, so as to prevent overheating. 



Note. — -The agar may be soaked in cold water over night. 

 This removes some of the impurities and renders the agar more 

 readily soluble. 



4. Add 3 grams extract of beef and 10 grams Witte's 

 pepton. 



5. Adjust the reaction. 



6. Adjust the weight. Place 1,000 grams weight 

 and the weight of the saucepan on one side of the scales 

 and then add enough water to make the saucepan with 

 the agar balance. If the weight is too high, it should 

 be boiled gently until the weight has been brought 

 down to the proper amount. 



7. Make a paper filter as described below and 

 arrange a retort stand as illustrated in Fig. 12. 



8. When at the boiling point filter the agar and dis- 

 tribute into culture tubes. 



9. The tubed agar should be sterilized in the auto- 

 clave for 5 minutes. 



For agar slants each tube should contain about 7 c.c. 

 or be filled one-third of the length of the tube. For 

 plating, the tube should be half filled and contain 10 

 c.c. Slants are prepared by allowing the agar after 

 sterilization to cool in a slanting position. If it is de- 

 sired to slant a large number a whole basket may be 

 put in a slanting position. When a few tubes only 



