DECOLORIZING ■ SOL VTIONS. 1 43 



trated. Prepare a cover-slip preparation, dry it care- 

 fully, fix it, and without allowing water to get on it 

 from any source, attempt to stain it with a solution 

 of the dyes in absolute alcohol, washing it out subse- 

 quently with absolute alcohol ; the result is negative. 

 The absolute alcohol does not possess the property of 

 diffusing into the dried tissues, and hence, as has been 

 stated before, alcoholic solutions of the staining dyes 

 should not be employed. The staining dyes should 

 always be watery." 



Decolorizing Solutions. — As regards the employ- 

 ment of decolorizing agents, it must always be borne in 

 mind that objects which are easily stained are also easily 

 decolorized, and those that can be caused to take up the 

 staining material only with difficulty are also very diffi- 

 cult to rob of their color. The most common decolor- 

 izer in use is probably alcohol — not absolute alcohol, 

 but alcohol containing more or less of water. Water 

 alone has this property, but in a much lower degree 

 than dilute alcohol. On the other hand, a much more 

 energetic decolorization than that possessed by either 

 alone can be obtained by alternate exposures to alcohol 

 and water. More energetic in their decolorizing action 

 than either water or alcohol, are solutions of the acids. 

 They appear, particularly when they are alcoholic solu- 

 tions, to diffuse rapidly into tissues and bacteria and 

 very quickly extract the staining materials which have 

 been deposited there. For this reason these solutions 

 should be employed with much care. 



J In the iDeginning of this chapter it was stated that the saturated alcoholic 

 solutions of the dyes do not serve as stains for bacteria. It must be remem- 

 bered that this holds only when absolute alcohol and perfectly dry coloring 

 matters have been used. If but a small proportion of water is present, the 

 bacteria may be stained with these solutions. 



