156 BAOTEEIOLOQY. 



TaBuic acid solution in water (20 acid, 80 water) . . 10 c.o. 

 Cold saturated solution of ferro-sulphate .... 5 c.c. 

 Saturated watery or alcoholic solution of fucbsin , . 1 c.c. 



This solution represents the mordant. A few drops 

 of it are to be placed upon the film of bacteria on the 

 cover-slip, which is then to be held over the flame until 

 the solution begins to steam. It should not be boiled. 

 After steaming, the mordant is washed off in water and 

 finally in alcohol. The bacteria are then to be stained 

 in a saturated aniline-water-fuchsin solution. 



When treated in this way different bacteria behave 

 differently: the flagella of some stain readily in the 

 above solutions; others require the addition of an alkali 

 in varying quantities; while others stain best after the 

 addition of acids. To meet these conditions an exact 

 1 per cent, solution of caustic soda in water must be 

 prepared, and also a solution of sulphuric acid in water 

 of such strength that one cubic centimetre will be ex- 

 actly neutralized by one cubic centimetre of the alkaline 

 solution. 



For different bacteria which have been studied by 

 this method the one or the other of these solutions is 

 to be added to the mordant in the following propor- 

 tions. 



Of the acid solution: 



For tlie bacillus of Asiatic cholera . J^ to 1 drop. 



For the spirillum rubrum . 9 drops. 



Of the alkaline solution: 



For the bacillus of typhoid fever . . 1 c.c. 



For the bacillus subtilis . . 2S to 30 drops. 



For the bacillus of malignant oedema 36 to 37 " 



For other organisms one must determine whether the 

 results are better after the addition of acid or alkali, 

 and how much of either is required. In general, it may 



