126 CULTURE MEDIA AND THEIR STERILIZATION 



with all possible aseptic precautions and distributed to sterile test- 

 tubes. In these it is heated on a water bath or a special blood-serum 

 sterilizing and coagulating apparatus (Robert Koch) for five to seven 

 consecutive days for one hour at 60 C. During the intervals it is 

 always kept in a warm place. On the seventh or eighth day it is 

 treated as usual and then the temperature is slowly raised to 90 C. 

 and maintained at this height until the serum in the test-tubes is 

 firmly coagulated. The tubes, while in the Koch apparatus, are 

 kept in a slanting position. After removal from the apparatus they 

 are preserved in a cool place until needed. Blood serum may be ob- 

 tained from sheep, cattle, or swine, at a slaughter house, or it may be 

 drawn directly from the horse, sheep, or goat. In the former case it 

 should be collected in sterile glass receptacles when the bloodvessels 

 of the neck are cut and placed in the refrigerator with as little delay 

 as possible. The less these vessels are shaken the clearer a serum 

 may be expected. After having been on ice for from twenty-four to 

 forty-eight hours the serum has generally well separated from the 

 clot or coagulum. The former may now be poured or pipetted 

 off and distributed into sterile test-tubes or other sterile glass 

 receptacles. 



FIG. 58 FIG. 59 



Blood-serum coagulator. . Dry-heat sterUizer. 



Sterilization of Glassware. All glassware used for culture media 

 must be sterilized before use. This is best accomplished in a dry-air 

 sterilizer. The apparatus is constructed on the principle of a baking 

 oven as found in an ordinary kitchen gas stove or as a detached 

 kitchen utensil. In fact, a baking oven of this kind may be used 

 as a dry sterilizer. In bacteriological work the temperature for dry 

 sterilization may be raised to 160 to 200 C. Because new glassware 

 often contains a slight deposit of soluble alkalies, test-tubes, flasks, 

 etc., must be soaked in water acidulated with hydrochloric, nitric, or 

 sulphuric acid before being used for the first time and afterward 

 washed in pure water until every trace of acid has been removed; 

 otherwise the alkalies would subsequently enter the culture media 



