PREPARATION OF NUTRIENT GELATIN. 



LABORATORY WORK. Place 500 g. of chopped lean beef 

 into a clean 1^-2 litre flask; add 1000 c. c. of tap-water 

 and insert a cotton plug into the mouth of the flask. Shake 

 the flask repeatedly during the next 15-30 rain., and then 

 immerse in boiling water in a water-bath and heat for 

 15-30 min. Filter through muslin and to the filtrate or 

 meat extract thus obtained add, 



100 g. of gelatin 

 10 g. of dry peptone 

 5 g. of common salt. 



Warm in the water-bath until the gelatin melts, then 

 neutralize or render slightly alkaline by cautious addi- 

 tions of a saturated sodium carbonate solution (avoid 

 excess of alkali). Continue heating in a water-bath, with 

 occasional shaking, for f to 1 hr. Filter through a plaited 

 filter. The filtrate should be, (1) perfectly clear, (2) 

 should be neutral or slightly alkaline in reaction, (3) 

 should not become cloudy or coagulate when boiled in a 

 test tube for 1 to 2 minutes, (4) should solidify when 

 cooled. 



If the filtrate is cloudy and strongly alkaline correct 

 the reaction by the addition of dilute acetic acid. If it 

 becomes cloudy or coagulates when warmed, continue 

 heating in the water-bath. 



If the filtered gelatin answers the above requirements 

 then fill, with the aid of a small funnel, into test-tubes to 

 a depth of 1 to 1^ inches. Avoid touching the neck of 

 the tube with gelatin. These test-tubes are first 

 thoroughly cleansed, allowed to dry, then plugged with 

 cotton, placed upright in a wire basket and sterilized in a 

 dry heat oven at 150 to 175 C. for 1 hour. 



After the tubes have been filled with gelatin they are 

 again sterilized by heating in the steam sterilizer, (100 

 C.) for 15 minutes, each day, for the next consecutive 

 three days. 



