86 MICROSCOPICAL EXAMINATION OF BACTERIA 



mat, and cover it with an inverted watch-glass until 

 dry. 



6. Fix by immersing in one of the fixing fluids pre- 

 viously mentioned (vide page 82). 



7. Clear with acetic acid and alcohol. 



8. Stain and mount as an ordinary cover-slip film 

 preparation, being careful to perform all washing op- 

 erations with extreme gentleness. 



Microscopical Examination of the Unstained Speci= 

 mens. 



1. Place the body tube of the microscope in the ver- 

 tical position. 



2. Arrange the hanging-drop slide on the micro- 

 scope stage so that the drop of fluid is in the optical 

 axis of the instrument, and secure it in that position 

 by means of the spring clips. 



3. Use the |-inch objective, rack down the body 

 tube until the front lens of the objective is almost in 

 contact with the cover-slip that is, well within its 

 focal distance. This is best done whilst bending down 

 the head to one side of the microscope, so that the 

 eyes are on a level with the stage. 



4. Apply the eye to the ocular and adjust the plane 

 mirror to the position which secures the best illumina- 

 tion. 



5. Rack the condenser down slightly and cut down 

 the aperture of the iris diaphragm so that the light, 

 although even, is dim. 



6. Rack up the body tube by means of the coarse 

 adjustment until the bacteria come into view; then 

 focus exactly by means of the fine adjustment. 



Some difficulty is often experienced at first in rinding 

 the hanging drop, and if the first attempt is unsuccess- 

 ful, the student must not on any account, whilst still 

 applying his eye to the ocular, rack the body tube 

 down (for by so doing there is every likelihood of the 



