CHAPTER IV. 



THE CULTIVATION OF BACTERIA. 



Inoculation of the Tubes. — The air of the laboratory 

 should be as quiet as possible, in order to lessen the chances 

 of contamination by bacteria clinging to particles of dust. 

 Spores are blown from the surfaces of moulds like thistle- 

 down, and are constantly being wafted about in the air where 

 there are draughts. After the colonies are obtained on the 

 plate or in the Esmarch tube a pure culture is obtained by trans- 

 ferring a minute amount of the growth from a colony over into 

 a test-tube containing the sterile culture medium. The transfer 

 is effected by means of a straight platinum wire, or with a plati- 

 num wire loop. The platinum is to be sterilized by heating 

 to a red heat in the Bunsen flame or with an alcohol lamp before 

 using, and then allowed to cool. It is also to be heated red- 

 hot after using. The plug of the test-tube is withdrawn, 

 twisting is slightly, taking it between the third and fourth 

 fingers of the left hand, with the part that projects into the tube 

 pointing toward the back of the hand. It must not be allowed 

 to touch any object while out of the tube. The upper inch 

 or two of the tube should be passed through the flame in order 

 to destroy any bacteria which may settle on it from the air while 

 the plug is out. If any of the cotton adheres to the in- 

 side of the tube it should be removed with sterilized for- 

 ceps, while the neck of the tube touches the flame, so that 

 the threads of cotton may be burned and not fly into the 

 air of the room. The tube should be held as nearly hori- 

 zontal as possible. The tube should be held in the left 

 hand between the thumb and forefinger, resting upon the 



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