DECOLORIZING SOLUTIONS. 139 



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

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

 from any source, attempt to stain it with a solution of 

 the dyes in 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 decolorizer 

 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 de- 

 colorization 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 ap- 

 pear, particularly when they are alcoholic solutions, 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 em- 

 ployed with much care. 



' In the beginning of this chapter it was stated that the saturated 

 alcoholic solutions of the dyes do not serve as stains for bacteria. 

 It must be remembered 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. 



