Saturated alcoholic solution of methylene blue 3 volumes. Caustic potash, aqueous solution 1 : 10,000 10 volumes. Filter. This solution is perhaps the most generally useful stain. It colours most bacilli and micrococci, and while rapid in its action rarely overstains. It must be made up fresh on each occasion. It is the best counterstain after staining tubercle bacilli, &c., with fuchsine. *Ziehl’s carbol-fuchsine.* _Carbolic acid_ (5 per cent. aqueous solution) 100 volumes. _Fuchsine_ (saturated alcoholic solution) 11 volumes. The solution must be filtered immediately before being used. *Gram’s iodine solution.*--Sections are placed in this solution after being stained with aniline dyes. The iodine in some way fixes the dye in the organisms, so that they are not decolourised along with the rest of the tissues. It is made thus:-- Iodine 1 grm. 1-1/2 grains. Iodide of potassium 2 grms. 3 grains. Distilled water 300 c.c. 1 ounce. Ten per cent. aqueous solutions of *nitric* and *sulphuric* acids should be prepared and may be kept indefinitely. The following are the general methods of employing these reagents for the purpose of staining organisms in sections. Special methods are required for special organisms, but one or two only can be given. *Weigert’s method.*--The sections must be placed in a freshly made one per cent. aqueous solution of methyl violet, gentian violet, fuchsine, &c. The solution may be kept at the temperature of the body in an incubator. The organisms will often stain more readily if the section be passed through a 1 in 2000 solution of corrosive sublimate before putting it into the staining fluid. After staining the section is washed in distilled water and then in methylated spirit until it appears almost decolourised. Some prefer to decolourise the tissues by washing in a half per cent. solution of acetic acid instead of methylated spirit. Practice is required before the correct time for decolourising is accurately estimated. The beginner should float a section rapidly on the slide now and then, put on a cover-glass and examine it under a low power to see if the decoloration has been carried far enough. A contrast stain may then be used, such as picrocarmine, after which the section may be mounted in Farrant’s medium: or a weak solution of another aniline colour may be used as a counter stain, after which the section is clarified in xylol, and mounted in balsam dissolved in xylol.