46 TEXT-BOOK OF BACTERIOLOGY. 



An anilin-water gentian-violet solution or an anilin-water fuchsin 

 solution is mixed with \% hydrate of sodium, in the proportion of 

 1 : 100 (1 cm. of the staining- solution). The coloring- matter is 

 thereby brought to the verge of separation, and in this state de- 

 velops a high staining power. 



We have by no means exhausted all the combinations of color 

 nor all the directions for staining with which our investigators 

 have enriched this branch of research, but it would lead tco far 

 should we attempt to go more into detail. 



Only one more means to increase the action of our dyes will be 

 mentioned, and that is the warming of the solutions while they are 

 being used. The coloring substance when warmed penetrates very 

 much more quickly and energetically into the objects, the tissues 

 as well as the bacteria take a stronger and more distinct staining, 

 the stain lasts better and becomes less soluble. 



This means cannot, of course, be employed in all cases. Cover- 

 glass preparations bear the heating well, and with them the process 

 can be employed without damage so far as to cause the formation 

 of bubbles and even boiling of the fluid. This can best be managed 

 by taking the cover-glass with forceps, letting a few drops of the 

 staining solution fall on it, and holding the preparation, with the 

 fluid, immediately over a flame. Vapors soon rise and ebullition 

 follows; if we supply an occasional new drop, to replace what is 

 lost by evaporation, the process can be continued indefinitely. 



Sections, on the other hand, are apt to be destroyed by such 

 treatment; they fall apart and become useless. Here, then, it is 

 better not to attempt the warming, but to stain for a longer time 

 in cold solution. 



If a preparation be now stained with one of the already de- 

 scribed coloring matters, we must first remove the superfluous dye- 

 stuff that has not been thoroughly imbibed before proceeding to 

 examine it. In this way alone can a clear picture be obtained, 

 showing distinctly the differences which the staining is intended to 

 develop. 



To do this we chiefly employ water and alcohol; both dissolve 

 the pigments, and thus they gradual^ withdraw the stain from 

 the preparations. In very many cases water suffices, and if the 

 washing is continued sufficiently long, the extra color will be so far 

 removed as to leave what are called "well-differentiated" prepara- 

 tions. 



We often endeavor to supplement the decoloring power of the 

 water or the alcohol, and give it a special action by the addition of 

 acids. 



