CHAPTER II. 

 CULTURE MEDIA. 



WHILE there are certain advantages in sterilizing the glass test- 

 tubes prior to filling them with media, yet this may be dispensed with 

 the sterilization after the media has been tubed being sufficient. If a 

 dressing sterilizer is at hand, this is preferable for sterilizing such 

 media as bouillon, potato and agar (10 to 15 pounds' pressure for 

 fifteen .minutes) . Milk shculd be sterilized with the Arnold, subjecting 

 the media to three steamings for twenty minutes on three successive 

 days. Gelatin may be sterilized in either way, but preferably in the 

 autoclave at 7 pounds' pressure for fifteen minutes. As soon as taken 

 out of the sterilizer it should be cooled as quickly as possible in cool 

 water. . This procedure tends to prevent the lowering of the melting- 

 point of the finished gelatin and also preserves its spissitude. 



Blood-serum is preferably solidified as slants in a blood serum 

 inspissator. This requires one to two hours. The subsequent sterili- 

 zation in the autoclave or Arnold should not be done immediately 

 after making the solidified slants, but on the subsequent day. If 

 done on the same day, many of the slants are ruined by being dis- 

 rupted by bubbles. The preparation of blood-serum slants or slants 

 of egg media can be conveniently carried out in a rice cooker (double 

 boiler). Place the tubes in the inner compartment of the cooker, 

 obtaining the slant desired by manipulating an empty test tube, or 

 with a towel or cotton batting on the bottom. Then cover the tubes 

 with another towel. The outer compartment should contain water 

 alone '(no 25% salt solution). The inner compartment should be 

 weighied down so that it is surrounded by water the light tubes not 

 being sufficient to sink it. Allowing the water in the outer compart- 

 ment to boil one or two hours will inspissate or solidify the slants 

 satisfactorily. The sterilization on subsequent days may be carried 

 out in the same apparatus, although it is more efficient if done in an 



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