24 PRACTICAL BACTERIOLOGY 



2. Crush the material with a second slide laid crosswise. 



3. Heat over the flame until the acetic acid cooks. 



4. Separate the two slides and dry over the flame. 



5. Remove fatty substances with ether. 



6. Cover the prepared surfaces with solution A, and heat over the 

 flame until vapour arises. 



7. Wash with water. 



8. Decolorize in solution B, three or four seconds. 



9. Wash with water. 



10. Dry with filter paper and over the flame. 



11. Mount in xylol balsam. 



The fungi are stained a deep blue colour, while epithelial structures, 

 owing to the glycerine-ether mixture, appear green. If this differentia- 

 tion is not desired, the decolorization with glycerine-ether can be 

 dispensed with. 



XX. ORDINARY METHOD OF EXAMINING MILK FOR 

 BACTERIA IN COVER-GLASS SPECIMENS. 



1. Dip a sterilized platinum wire into the milk, and draw the wire 

 sharply across the surface of a clean cover-glass. 



2. Air dry, and fix in the flame. 



3. Hold the cover-glass between the fingers, and flood the prepara- 



tion side with some sulphuric 

 ether to remove the fat. 



4. To demonstrate ordinary 

 bacteria stain with methylene 

 blue, as it does not colour 

 the background so intensely as 

 fuchsin or gentian violet. To 

 demonstrate Tubercle bacilli, 

 stain the specimen according 

 to the special method given 

 on page 21. The centrifugal 

 machine can also be used 

 (see Fig. 7), and the resulting 

 sediment examined, the same 

 way as ordinary milk. 



The advantages of the cen- 

 trifugal machine are that 

 FIG. 7. Aitmann's Hand Centrifuge. sedimentation can be carried 



out very quickly, and the discovery of Tubercle bacilli rendered easier. 



