8 INTRODUCTION 



Ex. 7. Prepare the following solution : 



Loffler's Methylene Blue. 



(1) Make up a i per cent, solution of caustic potash. 



(2) Take i c.c. of it and add it to 100 c.c. of distilled water. 



(3) Mix weak solution (2) with 30 c.c. of a saturated alcoholic 

 solution of methylene blue (Ex. 6). Shake, filter into a 

 stoppered bottle, and label it. 



This is an excellent stain, not very deep, but it often brings 

 out delicate features of bacteria; it loses some of its staining 

 power on keeping. Try it on cover-glass preparations as 

 described in Ex. 5, allowing it to act for 3-10 minutes. 



Ex. 8. Prepare the following solution : 



Ziehl-Neelsen's Carbol-fuchsin. 



Fuchsin . . .... . . i gr. 



Absolute alcohol . . ,~ 10 c.c. 



Carbolic acid (crystals) . .- 5 g r - 



Distilled water . . . . . .100 c.c. 



Dissolve the fuchsin in the alcohol in a mortar or porcelain 

 dish, breaking the fuchsin if necessary with a pestle or a glass 

 rod. Then dissolve the carbolic acid in the water and add half 

 of this solution to the dye in the mortar or dish ; stir well, and 

 pour into a stoppered bottle. Wash out the mortar with the 

 rest of the carbolic-acid solution, adding it to the mixture in the 

 bottle. Shake well, and after twenty-four hours filter it into an 

 amber-coloured stoppered bottle or ordinary glass bottle covered 

 with brown paper to exclude the light. 



This gives an intense red stain. It is best to use a freshly 

 prepared weak solution made by adding i c.c. of the above 

 concentrated solution to 10 c.c. of distilled water; filter. Try 

 it on cover-glass films as described in Ex. 5, allowing it to act 

 for 1-3 minutes. 



Ex. 9. Gram's Method of Staining. Prepare the following 

 solutions : 



