28 ESSENTIALS OF BACTERIOLOGY 



is preferable to examine bacteria, when possible, in their natu- 

 ral state. 



We obtain the bacteria for examination either from liquid or 

 solid media. 



From Liquids. With a long platinum needle the end of 

 which is bent into a loop (Fig. 9, a) obtain a small drop 

 from the liquid containing the bacteria, and place it on a cover- 

 glass or slide, careful that no bubbles remain. 



Sterilize Instruments. Right here we might say that it is 

 best to accustom one's self to pass all instruments, needles, 

 etc., through the flame before and after each procedure; it 

 insures safety; and once in the habit, it will be done automati- 

 cally. 



From Solid Media. With a straight-pointed platinum 

 needle (Fig. 9, b) a small speck of the medium is taken and 



Fig. 9. Platinum needles for transferring bacteria made from No. 27 

 platinum wire inserted in glass rods: a, Looped needle; b, straight-pointed 

 needle (McFarland) 



rubbed upon a glass slide with a drop of sterilized water or 

 bouillon, and from this a little is taken on cover-glass, as before. 

 The cover-glass with its drop is now placed on the glass slide, 

 carefully pressing out all bubbles. Then a drop of cedar-oil is 

 laid on top of the cover-glass, and the oil-immersion lens dipped 

 gently down into it as close as possible to the cover-glass, the 

 narrow blender shutting off the Abbe condenser, for this being 

 an unstained specimen, we want but little light. We now apply 

 the eye, and if not in focus, use the fine adjustment or the 

 coarse, but always away from the object i. e., toward us 

 since the distance between the specimen and the lens is very 

 slight, it does not require much turning to break the cover- 

 glass and ruin the specimen. Having found the bacterium, 

 we see whether it is bacillus, micrococcus, or spirillum ; discover 

 if it is motile or not. That is about all we can ascertain by 

 this method. 



