14 GENERAL BACTERIOLOGY 



EXERCISE 7. PREPARATION OF GELATIN. 



GENERAL DIRECTIONS. 



Same as bouillon (4). 

 c. 



d. Add \% peptpne, 0.5% salt and 10-15 %* of the best gold 

 label, sheet gelatin, and weigh. 



e. Heat until ingredients are dissolved. 

 /. Neutralize. 



g. Boil 5 minutes and restore weight. 



h. Test reaction. 



i. Boil until albumin coagulates and floats in the clear fluid. If 

 beef extract is used it will be necessary to first cool below 60 C. 

 and thoroughly stir in an egg. 



j. Filter. Arrange the apparatus 

 shown in Fig. 5. Use absorbent cotton. 

 The funnel and flask should first be heated 

 with warm water. Usually the hot gelatin 

 will filter without the use of the pump. If 

 the pump is needed it should be started be- 

 fore pouring in the culture medium. This 

 prevents the unfiltered gelatin from pass- 

 ing between the cotton and glass. 



Jc. Add 5.0 cc. (0.5 %) of a normal hy- 



, 1 -I i i , FIG. 5. Apparatus for fllter- 



arOCnloriC acid. SOlUtlOn. ing media through absorbent 



7 m v /K\ cotton; a, coil of wire over 



I. lUDe. (D). laid with layer of absorbent 



, .,. . ^ OA cotton; b, tubes for making 



m. Sterilize in the Steamer for 20 connection with air pump; c, 



minutes on three consecutive days or in the ^ance^/waterlnto^Isks. er 

 autoclave at 110 C. for 15 minutes. 



REFERENCES. A. 99 ; H. 47 ; M. & R. 40 ; McF. 184 ; P. 215 ; 

 P. B. C. 26. 



SPECIAL DIRECTIONS. Make 1 liter, using method A. Fill 30 

 test-tubes. Put the remainder in flasks, sterilize in steam sterilizer 

 or autoclave. Remember long exposure to high heat injures the 

 solidifying properties of gelatin. 



1 The amount to be varied according to the season of the year, 10 per cent, 

 in winter, 12-15 per cent, in summer, but it should be remembered that differ- 

 ent quantities affect the appearance of the cultures. 



