PREPARATION OF STAINS. 81 



sinuous, undulating, or rotary movement. It is impossible to 

 see the flagella. 



When the examination has been completed, the slide and 

 cover-glass are dropped into a 5 per cent, carbolic acid solu- 

 tion and left there for one hour. Disinfection by heat is dan- 

 gerous, because the drop is very apt to sputter and thus be 

 the means of carrying infection. 



PREPARATION OF STAINS : The anilin dyes are used almost 

 exclusively for the staining of bacteria. Those manufactured 

 by Gruebler are the most reliable, and should always be spe- 

 cified when dry stains are ordered. The most widely used 

 stains are gentian-violet, methylene-blue, fuchsin, vesuvin, 

 and malachite-green. So-called stock solutions of these stains 

 should always be on hand. From these, small quantities of 

 stain are prepared for immediate use, as they deteriorate very 

 rapidly. They are kept in small bottles supplied with stop- 

 pers and pipettes (Fig. 33). Yesuvin and malachite-green are 



FIG. 33. 



Rack of bottles for staining solutions. 



kept in 1 per cent, aqueous solution. -Of all the other stains 

 alcoholic stock solutions are made. Aqueous stock solutions 

 can be prepared when needed. The stock solutions are made 

 by adding 1 part of the powdered dye to 4 parts of abso- 

 lute alcohol. A glass-stoppered bottle is filled to one- 

 quarter of its capacity with the dye, and sufficient absolute 

 alcohol (or water for aqueous solutions) added to fill the 

 bottle. An excess of the dye may be used to insure satura- 

 tion ; the excess remains undissolved in the bottom of the 



6-Bact. 



