154 BACTERIOLOGY. 



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. 1 



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. 



Very dilute acetic acid robs tissues and bacteria of 

 their staining with remarkable activity ; still more ener- 

 getic are solutions of the mineral acids, and particularly, 

 as has been said, when this action is accompanied by 

 the decolorizing properties of alcohol. 



1 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 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. 



