METHOD OF EXAMINING CULTURES 23 



METHOD OF EXAMINING CULTURES 



Requisites. — i. Clean slides and cover-glasses. (These must 

 be the thinnest in ordinary use — i.e.. No. i.) 



2. A platinum needle (straight or loop). 



3. A Bunsen burner or a spirit-lamp with a tall flame. 



4. The stain to be employed (see p. 30). 



5. Canada balsam dissolved in xylol. This should be bought 

 ready for use. 



6. A pair of dissecting forceps. 



7. Strips of white blotting or filter paper. 



Process. — i. Sterilize the needle, and place a small drop of water 

 (preferably distilled) in the centre of a clean slide. 



2. Take the culture-tube in the left hand between the index and 

 middle fingers with its mouth directed to the right and (in the case 

 of a culture on a solid medium) slightly downward. 



3. Burn the surface of the plug in the flame. Remove the plug 

 with the forceps (previously sterilized by being passed slowly 

 through the flame), and place it between the ring and little fingers 

 of the left hand. Lay the forceps down. 



In cases where you are examining the culture for diagnostic 

 purposes only, and do not care if it becomes contaminated during 

 the process, it is unnecessary to take these precautions. The 

 cotton-wool plug may then be removed with the fingers and laid 

 down on the table. As a matter of fact, very few cultures do 

 become contaminated, even if no precautions are taken. 



4. Sterilize the needle in the flame and allow it to cool. 



5. Now introduce the needle into the tube, and take up a small 

 portion of the growth, taking care not to scrape up the surface of 

 the medium as you do so. Most beginners fall into the mistake 

 of taking up far too much of the growth, and preparing a film 

 which is spread so thickly that the individual bacteria cannot be 

 distinguished. 



6. Take the plug up in the forceps, burn its surface in the 

 flame, re-plug the tube and lay it down. 



7. Stir the droplet of water which has been deposited on the 

 slide with the tip of the needle, so that the bacteria which it 

 carries are mixed with the water. Now spread out the emulsion 

 thus produced so as to form a patch about A inch in diameter. If 

 it does not spread out uniformly it is a sign that the slide is not 

 clean. 



