182 BACTERIOLOG Y. 



alone has this property, but in a much less degree than 

 dilute alcohol. On the other hand, a much more ener- 

 getic 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 solutions, 

 to diffuse rapidly into tissues and bacteria and very 

 quickly extract the staining-materials Avhich 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 stain 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. 



The acid solutions commonly employed are : 



Acetic acid in from 0.1 to 5 per cent, watery solution. 



Nitric acid in from 20 to 30 per cent, watery solu- 

 tion. 



Sulphuric acid in from 5 to 10 per cent, solution in 

 water. 



Hydrochloric acid in from 1 to 3 per cent, solution in 

 alcohol. 



STAINING OP BACTERIA IN TISSUES. 



In staining tissues for the purpose of demonstrating 

 the bacteria which they may contain a number of points 

 must be borne in mind : the conditions which favor the 

 diifusion of the staining-fluids into the bacteria are now 

 not so favorable to rapid staining as they were when 

 the bacteria alone were present upon cover-slips ; the 

 staining of tissues, therefore, rccjuires a longer exposure 



