STAINING OF FLAGELLA 91 



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, 

 may be broken off. Small drops of water are placed on a 

 number of perfectly clean cover-glasses, and each of these 

 inoculated with a trace of the dilution, which is gently 

 spread over the cover-glasses. Better results are obtained 

 by diluting a broth culture about twenty-four hours old. 

 Tap-water should always be used for diluting, as the micro- 

 organisms are so extraordinarily sensitive that they often 

 cast off their flagella if placed in distilled water. 



The prepared cover-glasses are now allowed to dry in the 

 air spontaneously. The ' fixing ' must then be done with 

 great care by passing through the flame three times, by 

 holding the cover-glass in the fingers instead of the forceps, 

 as the temperature which is endured by the fingers does 

 not injure, but is quite sufficient for the purpose. The 

 preparations are now treated by one of the following 

 methods : 



Lqffler's Method. — It is to Dr. Loffler that we are indebted 

 for the following method, which he devised as the result of 

 a long and tedious investigation. This process, when care- 

 fully carried out, gives very fine results. Loffler found that 

 some organisms require an alkaline, and others an acid, 

 mordant ; and, again, the exact amount of alkalinity or 

 acidity varies according to the particular organism under 

 investigation. To render the mordant alkaline, he recom- 



