82 MICROSCOPIC EXAMINATION OF BACTERIA. 



bottle. The stains are prepared from these stock solutions 

 by adding 5 c.c. of the solution to 95 c.c. of distilled water ; 

 or the stock solution is added to the water drop by drop until 

 a good color is produced. The first method is preferable, as 

 it is more exact. 



Loeffler's alkaline methylene-blue is made as follows : 



Saturated alcoholic solution of 



methylene-blue, 30 c.c. ; 



Caustic potash (1 : 10,000), 100 " 



This stain is always used for staining the diphtheria bacillus. 



The anilin-water stains are prepared as follows : 5 c.c. of 

 anilin oil are shaken thoroughly with 100 c.c. of distilled 

 water. This solution is filtered through filter-paper until it 

 is perfectly clear. To 100 c.c. of the filtrate add 10 c.c. of 

 absolute alcohol and 11 c.c. of the concentrated alcoholic 

 solution of the stain. The anilin-water stains are used where 

 a very strong stain is required. They are decomposed easily, 

 however, and should be prepared in small quantities only. 

 The anilin water may be kept on hand, so that the stain can 

 be prepared rapidly when needed. 



STAINING SLIDES AND COVER-GLASSES : Bacteria may 

 be examined on a slide or a cover-glass. Cover-glasses, 

 because of their size, can be placed in the stain, but slides 

 are handled more easily. They should be absolutely clean 

 and free from fatty matter. First immerse them in a mineral 

 acid or a mixture of sulphuric acid and potassium bichro- 

 mate ; then in successive washings of water, alcohol, and 

 ether. They are kept in ether until ready to be used. If 

 desired, they may be kept in alcohol, when the ether washing 

 is omitted. For use, they are wiped dry 'with a piece of 

 cheese-cloth and passed a few times through the flame of an 

 alcohol lamp or Bunsen burner. 



For convenience we will consider the preparation of a slide 

 (the cover-glass is prepared in the same way) : 



Spread the material on the slide as thinly as possible. 

 Students usually make the mistake of spreading it too thick 

 for fear that there is not sufficient on the slide. The thinner 



