212 BACTERIOLOGY 



up from a yellow purulent spot by means of a platinum 

 needle with the point flattened like that of a scalpel, and 

 which has previously been sterilised at a red heat ; this 

 particle is rubbed between two cover-glasses, which are 

 then passed three times through the flame. Staining is 

 done with an aniline water solution of gentian violet which 

 has first been warmed, and the preparations are decolorised 

 by transferring them from the gentian violet, as soon as it 

 has grown cold, to a hydrochloric acid alcohol containing 

 20 parts water and 2 parts hydrochloric acid to 100 parts 

 alcohol. The preparations remain in this mixture for half 

 a minute to a minute, are then transferred to concentrated 

 alcohol for the same length of time, and afterwards rinsed 

 in water. They are now dried and placed for a half to one 

 minute in a filtered concentrated solution of vesuvine in 

 water by way of double-staining, rinsed in 96 per cent, 

 alcohol, and brought under the microscope in a drop of 

 water. The tubercle bacilli appear of a dark violet colour, 

 or even nearly black, as the aniline brown absorbs the 

 blue part of the spectrum, so that a blue object must seem 

 black in a brown solution. The other portions of the 

 preparation are brown. 



The following is the method employed by Giinther : — 

 The cover-glass, having been prepared with sputum and 

 fixed in the flame, is deposited face downwards in a watch- 

 glass filled with solution of fuchsine in aniline water, the 

 centre of which is now heated over a very small flame while 

 being kept moving vertically up and down. When the 

 fluid begins to give off bubbles, heating is stopped, the 

 -watch-glass placed on the table, and let stand for a minute. 

 The process of heating is repeated about five times with 

 intervals of one minute's standing, after which the cover- 

 glass is taken from the stain and laid with the film of 

 sputum uppermost in a watch-glass containing 3 per cent. 



