CHAPTER VI 

 BACTERIOLOGICAL LABORATORY TECHNIC 



In order to study bacteria by other methods than the simple 

 examination of their morphology by means of stains, and by the 

 hang-drop, or block method, they must be cultivated either in 

 the bodies of experiment animals, or in culture media artificially 

 prepared. The latter method is the most widely used in labora- 

 tories. It is necessary, in order to study bacteria, that the media 

 shall not contain any extraneous bacteria to begin with, and 

 that they shall be cultivated under such conditions that such 

 bacteria cannot reach the media at any time. To accomplish all 

 this, the culture media must be kept in glass vessels, such as test- 

 tubes and flasks that have been sterilized. And, since all animal 

 and vegetable substances, not actually alive, are teeming with 

 a multitude of bacteria, these substances must be sterilized too, 

 in order that the media shall be free from any living organisms. 



Glassware is cleaned by boiling with soap suds or powder or if 

 very dirty by immersion in saturated watery solution of bichro- 

 mate of potash plus an equal part of sulphuric acid. This latter 

 must be very carefully washed away in running water. 



Glassware, such as pipettes, Petri dishes, flasks and test-tubes, 

 are sterilized best by dry heat in hot-air sterilizers. The appara- 

 tus is subjected to a temperature of i5oC. for one hour, or until 

 the cotton plugs are slightly brown. The glassware should be 

 put in wire baskets and the test-tubes should be kept erect. 

 Petri dishes are best sterilized in a wrapping of paper. Flasks 

 and test-tubes* are always plugged with raw cotton, which pre- 

 vents the ingress of bacteria, while air can reach the media 

 through it freely. 



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