STAINING OF FLAGELLA 95 



culture medium. After the preparation has been thoroughly 

 dried in the air, it should be held over the flame with the 

 fingers, as Loffler has directed. Afterwards the stain is 

 gradually poured on the slip and heated gently, the fluid 

 being brought almost to boiling-point ; the slip, covered 

 with the hot stain, should then be laid aside for one minute, 

 washed in water, and mounted. Upon examination, the 

 bacteria, both isolated and in clumps, will, if motile, be 

 found to have the flagella clearly and delicately defined. 

 In the middle of the cover-slip, as well as round the edges, 

 the bacteria will be found equally well stained, the clumps 

 being surrounded by a zone of delicate fringing flagella, 

 each being well stained and distinctly outlined from its 

 fellows. If a clear preparation is desired, the stain, after 

 mixing, may be filtered ; but Dr. Pitfield has found that the 

 most reliable method is to use the unfiltered stain. In the 

 case of the former, a clear fluid is produced without the 

 detritus, etc., being precipitated on the glass around the 

 micro-organisms, and all the flagella are stained, but not 

 so distinctly as with the unfiltered solution. If the filtered 

 stain is used, a second stain of aniline water, containing 

 gentian violet, had better be used, which should be applied 

 but a moment and then washed off, thus leaving a clean 

 field, showing only the bacteria lightly stained, with their 

 flagella still more lightly coloured. In examining the 

 different bacteria. Dr. Pitfield found that the bacillus of 

 typhoid fever, the colon bacillus, the cholera bacillus, and 

 the bacillus of hog cholera, each stained well by this 

 method, and without the addition of any acid or alkali to 

 the mordant such as LofBer uses. The bacillus of typhoid 

 fever showed the flagella most beautifully, and there seemed 

 one flagellum to each cell that stained more deeply than the 

 others and appeared larger and stronger. 



