STAINING OF FLAGELLA 89 



fuchsine is added to 20 c.c. of a 10 per cent, ammonia 

 solution contained in a dish. The solution is heated until 

 steam just commences to rise. The prepared cover-glasses 

 are then immersed in a solution for from three to ten 

 minutes, removed to a 20 per cent, solution of sulphuric acid 

 to decolourise, washed in water, and finally counter-stained, 

 as in the method given above. 



Staining of Flagella. — The flagella or organs of motion 

 which are attached to many bacilli and to some micrococci 

 are much more difficult to demonstrate by staining than 

 spores. In order to reveal the presence of these delicate 

 whip-like processes, it is necessary to have recourse to a 

 complicated and ingenious method of standing, as they 

 cannot be stained by any of the methods already described, 

 as the flagella do not possess any affinity for dyes unless 

 they are previously prepared with a ' mordant,' or a fixing 

 material to enable the flagella to subsequently fix tlie dye. 

 The following points must be carefully attended to in order 

 to obtain satisfactory results : The cover- glasses must be 

 absolutely clean, in which case a drop of water will spread 

 itself evenly over the surface, and will not run back or 

 refuse to adhere to any portion of it. The smallest particle 

 of grease or dirt will absolutely prevent any satisfactory 

 result being arrived at. No trace of nutrient medium should 

 be transferred to the cover-glass, or the result will be the 

 same as if the cover-glass were dirty ; and, owing to the 

 particles becoming stained, they may completely conceal the 

 faintly-stained flagella. Great care must be taken not to 

 have too many organisms on the cover-glass. The best 

 way to proceed is as follows : A trace of the microbic layer 

 from a fresh agar culture is mixed very carefully and 

 quickly with a drop of ordinary tap-water upon a slide, 

 rubbing the material as little as possible against the slide, 

 as the organs of movement, which are extremely delicate. 



