I40 PRACTICAL BACTERIOLOGY. 



for about a minute^ after which, it should be thoroughly 

 rinsed under a tap, or with a wash bottle, in order to 

 completely free it from the remains of the mordant. 

 Small particles of the mordant are apt to cling very 

 closely, especially on the edges of the cover-glass ; if 

 this should occur, it is best to wash the cover-glass in 

 absolute alcohol until they completely disappear. The 

 alcohol soon evaporates in the air, and then the cover- 

 glass ought to appear clear, except for the portion 

 which is covered by the layer of material containing 

 the bacteria; this should be grey or reddish grey. 



The most suitable solution for staining is the aniline 

 water solution of fuchsine, prepared as described on 

 p. Ill; a few drops are passed through a filter directly 

 on to the cover-glass until it is completely covered, 

 as it was with the mordant. It is then similarly 

 warmed for about a minute, and afterwards thoroughly 

 washed for a long time with a stream of water, until 

 no more colouring matter disengages itself. This 

 may sometimes take a long time, but is absolutely 

 necessary if the preparations are to be faultless. 

 The cover-glass can now be examined with the 

 microscope. 



If the preparation is successful, the bacteria are of a 

 very dark red, almost black colour, and also appear 

 much thicker than when stained in the usual manner; 

 this is because by this method their gelatinous 

 sheaths, which previously remained unstained, are 



