BACTERIA 



wards. If we now examine our slide under a high 

 magnification, we shall easily be able to see whether 

 bacteria are present or not. Should our preparation 

 be too deeply stained, a good slide will show the 

 bacteria stained blue against an almost colourless 

 background, we must immerse our second prepara- 

 tion for a few moments in a little of the J per cent, 

 acetic acid which will have the effect of removing 

 the excess of stain ; then, after washing and drying, 

 we proceed as before. 



Beautiful double staining may be performed by 

 the following method. In addition to the chemicals 

 we already possess we shall require some 5 per cent, 

 acetic acid. Double staining is especially useful for 

 spore-forming bacteria, so we may take some of the 

 Hay Bacillus at sporing time. Proceed exactly as 

 described above substituting, of course, a drop of 

 water known to contain the bacilli for the drop of 

 milk. When the two cover slips are ready for 

 staining, warm some of the Carbol-Fuchsine in a 

 saucer and leave the cover slip therein for five 

 minutes, then transfer to a 5 per cent, solution of 

 Acetic Acid till all the stain appears to be removed, 

 afterwards wash in water. The cover slips must 

 next be immersed for a few minutes, two should be 

 long enough, in Methylene blue solution, then 

 washed and, when dry, mounted on a slide with 

 Canada Balsam, as described above. If the stain- 

 ing has been properly carried out, we shall have 

 a most beautiful preparation, showing spores stained 

 red and the rest of the bacilli blue. 



164 



