CHAPTER IV. 



THE METHODS OF SOWING AND CULTIVATING 

 AEROBIC ORGANISMS. 



Introduction. 



Section I. Instruments used for sowing cultures, p. 67. 



Section II. The methods of sowing cultures, p. 70. 



Section III. Conditions essential to satisfactory growth, p. 72. 



Section IV. The examination of cultures, p. 73. 



Section V. Methods of storing cultures, p. 75. 



AEROBIC organisms should be grown in vessels which while allowing free 

 access of air at the same time protect them from dust. 



Various types of culture vessels are in use : for instance test-tubes, circular 

 flat-bottomed flasks, flasks of various other shapes, Petri dishes, Soyka 

 dishes, etc. 



Cotton- wool is generally used as a protection from dust. More rarely 

 paper caps and occasionally glass covers are also employed. 



In sowing a culture, the following rules must be observed : 



1. The instrument used must be sterile. 



2. The material to be sown must be collected without introducing extraneous 

 organisms : 



3. And must be transferred uncontaminated to the medium it is proposed 

 to sow. 



SECTION I. INSTRUMENTS USED FOR SOWING CULTURES. 



Cultures can be sown with a Pasteur pipette, platinum wire, or glass 

 needle. 



A. Pasteur pipettes. 



This consists of a piece of glass tubing drawn out in the blow-pipe, and 

 sealed at the pointed end, the other end being plugged with cotton-wool. 

 The pipette should be about 20 to 25 cm. long. 



A number of these pipettes ready sterilized should always be at hand. 



To make a Pasteur pipette. 1. Take a piece of glass tubing of 5 to 7 mm. 

 calibre (the size of a lead pencil), and with a file mark it off into lengths 

 of 25 cm. or thereabouts. (Glass tubing is sold in lengths of about 1 metre, 

 and each length should therefore cut up into four pieces.) 



2. Break the tubing by holding it in both hands and pressing the thumbs 

 against the glass, one on each side of a file mark. 



