DEC0L0RIZING-80LVTI0NS. 181 



SO readily when placed in water as when placed in 

 alcohol. 



The diffusion of staining-solutions in the protoplasm 

 of dried bacteria, as found upon cover-slip preparations, 

 is much greater and more rapid than ^^'hen the same 

 bacteria are located in the interstices of tissues. These 

 differences are not in the bacteria themselves, but in the 

 obstruction to diffusion offered by the tissues in which 

 they are located. The result of absence of diffusion 

 may easily be illustrated : 



Prepare a cover-slip preparation, dry it carefully, 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 subsequently with 

 absolute alcohol ; the result is negative. The abso- 

 lute alcohol does not possess the property of diffusing 

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

 alcoholic solutions of the staining-dyes cannot be satis- 

 factorily 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 made 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 



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

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

 must he remembered that this holds only when absolute alcohol and 

 perfectly dry coloring-matters have been used. If but a small propor- 

 tion of water is present, the bacteria may be stained with these solu- 

 tions, though the results are, as a rule, unsatisfactory. 



