CULTURAL TECHNIQUE 13 



undiluted medium. The reason for this is not known. Hence 

 the titration must be made after the addition of the first quan- 

 tity of N/lNaOH. Usually it will be found that a small 

 quantity of the N/l NaOH must be added. 



After neutralizing, cook thirty minutes over boiling water ; 

 then boil for two minutes over the free flame, stirring con- 

 stantly to prevent burning. Weigh and restore loss by evapo- 

 ration, allow the medium to stand several minutes in order 

 that the coagulated proteids may settle, filter through paper, 

 titrate, and record final reaction. If the reaction varies more 

 than 0.2 per cent either way from the normally accepted 

 standard (+ 1 per cent), it must be corrected. 



The finished product should have a pale straw color, be 

 perfectly clear, and on boiling a sample in a test tube should 

 show no further precipitation of proteid matter. Place in 

 flasks and tul><-s and sterilize in the autoclave. 



Summary : 

 Infuse meat. 



Weigh cooker and record weight. 

 Bring weight of infusion to 1000 grams. 

 Add 1 per cent peptone. 



Warm to dissolve peptone, not heating above 50 C. 

 Titrate and bring reaction to 4- 1 per cent. 

 Cook thirty minutes over boiling water. 

 Boil two minutes over free flame, stirring constantly. 

 Restore weight. 

 Allow coagulum to settle. 

 Filter. 



Test reaction and record. 

 Tube and sterilize. 



Exercise. Each student will prepare 1 liter of bouillon. 



