70 BACTERIOLOGY 



poured away, and the glass filled with aniline water ; a 

 solution is thus obtained which remains clear and stains the 

 bacteria themselves deeply, but the ground very slightly. The 

 cover-glasses should remain about half an hour in the stain- 

 ing fluid. 



Instead of the aniline water a 6 per cent, aqueous solution 

 of carbolic acid (phenol) may be used, to which an alcoholic 

 solution of fuchsine is added, until the mixture becomes of 

 a dark colour. This mixture is known as Ziehl's solutio7i, 

 and its composition is as follows : 



Crystallised carbolic acid . . 5'0 



Water 100-0 



Alcohol 10-0 



Fuchsine I'O 



According to Kiihne's formula, methyl blue instead of 

 fuchsine is mixed with 5 per cent, carbolic acid, water, and 

 alcohol, and a solution of strong staining power so obtained. 



Instead of carbolic solution a 1 per cent, solution of 

 ammonium carbonate can be used as a mordant. 



Koch employs a solution of caustic potash as an ingre- 

 dient, adding to 1 c.cm. of a concentrated alcoholic solution 

 of methyl blue 200 c.cm. of water and 0"2 c.cm. of a 10 

 per cent, potash solution, and Loffler also adds 100 c.cm. of 

 O'Ol per cent, solution of caustic potash to 30 c.cm. concen- 

 trated alcoholic solution of methyl blue. 



In certain staining processes, particularly that for tubercle 

 bacilli, a sidphuric acid solution of methyl blue is employed, 

 prepared by mixing 100 parts of a 25 per cent, solution of 

 sulphuric acid with 2 parts methyl blue ; or a nitric acid 

 solution consisting of a saturated solution of methyl blue 

 in 20 parts nitric acid, 30 parts alcohol, and 50 parts 

 distilled water. 



The different methods of staining are in many cases 

 assisted by heat, the colouring solutions being kept warm 



