Dissolve 5 grms. of hæmatoxylin crystals in 50 cc. of absolute alcohol; add this drop by drop, while stirring, to 1,000 cc. of a 1 per cent solution of potassium alum. Expose in open vessel to air and light for 1-2 weeks. Filter before using. b. =Hansen’s Haematoxylin.= To 200 cc. of alum-hæmatoxylin solution brought to the boiling-point add 2 cc. of a concentrated solution of potassium permanganate. Cool quickly; filter when cold. Can be used at once without further ripening. It tends to stain diffusely. c. =Delafield’s Haematoxylin.= To 400 cc. of a saturated solution of ammonia alum add a solution of 4 grms. of hæmatoxylin in 25 cc. of absolute alcohol. Expose mixture to air and light for 3-4 days; filter; then add 100 cc. of glycerin and 100 cc. of 95 per cent alcohol, and filter. Expose to light until solution is dark enough, then keep in tightly-stoppered bottle. It is a strong stain, and may be diluted with distilled water when desired. The solution keeps well. d. =Ehrlich’s Acid-haematoxylin.= Dissolve 2 grms. of hæmatoxylin in 100 cc. of absolute alcohol. Add this to a saturated solution of potassium alum in water 100 cc., glycerin 100 cc., and glacial acetic acid 10 cc. Allow mixture to stand for a week exposed to air and light; then filter. Keep in well-stoppered brown bottles. The solution stains best when it is six months old, and may be kept for several years. It does not overstain, and on the whole is more useful than Böhmer’s, Hansen’s or Delafield’s. e. =Mayer’s Haemalum.= Dissolve 1 grm. of hæmatein in 50 cc. of 90 per cent alcohol and warm. Add this solution to a solution of 50 grms. of potassium alum in 1,000 cc. of distilled water dissolved by heating. Mix warm, cool, and filter. With hæmatein no ripening is required, and the solution can be used at once. Hæmalum is a more precise nuclear stain, but stains more slowly than the formulæ given above. It may be prepared directly from hæmatoxylin crystals by dissolving 1 grm. of hæmatoxylin in boiling water; add water up to 1 litre, and cool. Add 0.2 grm. sodium iodate and 50 grms. potassium alum, dissolving at room temperature; 50 grms. chloral hydrate and 1 grm. citric acid may be added to make solution keep better. f. =Mayer’s Acid-haemalum.= Add 2 cc. glacial acetic acid to 100 cc. of hæmalum solution. It stains the nuclei more precisely than hæmalum. g. =Weigert’s Iron-haematoxylin.=