CHAPTER IV 

 STAINING METHODS AND STAINS 



When it is desired to make a microscopical examination 

 of a culture, the following procedure is adopted : Place on 

 a clean slide a drop of distilled water; take the culture- 

 tube between the index and middle finger of the left hand ; 

 remove the cotton plug and direct the mouth of the tube 

 downwards if the media is solid; sterilize a platinum 

 needle, and when cool pass it into the tube and pick off a 

 portion of a colony with the loop, taking care not to take too 

 much. Now heat the mouth of the tube with the flame ; 

 scorch the cotton plug, and thrust it into the test-tube. The 

 platinum loop, laden with bacteria, should be well mixed 

 with the drop of sterile water previously placed at one end 

 of the slide, and the bacterial emulsion thus made spread out 

 with the platinum needle laid flat on the slide, or a Wright 

 spreader may be used. Such a spreader is made as follows : 



Wright's Spreader. 



Take the thinnest possible slide, make a nick with a 

 glass-cutting knife * about halfway along its side; then grasp 

 the two ends between the finger and thumb of either hand, 

 and, advancing the thumb of the right hand as far as, or a 

 very little beyond, the intended line of fracture to serve as 

 a fulcrum, break the slide across by putting a transverse 

 strain upon it, at the same time exerting a pull in the 

 longitudinal direction. An arch is now formed ; the point 

 which is supported by the thumb will correspond to the 

 * To make a glass-cutting knife, see p. 47. 



