Histology FAQ

Staining, Histochemistry and Histotechnology

(Frequently Asked Questions)


Dr. John A. Kiernan
Department of Anatomy and Cell Biology
The University of Western Ontario
London, Canada



FAQ Home > Staining Methods, Histochemistry


McFaydean's stain for anthrax bacilli


What is M'Faydean's stain?


[This has been put together from three replies to a question raised on the HistoNet newsgroup.]

M'Faydean's stain is a simple stain using any well polychromed methylene blue (e.g. aged Loefflers). It is applied to heat-fixed smears for 10-30 seconds.

Polychroming (demethylation) is traditionally achieved by exposure of Loeffler's soln. to light and air for several months until it acquires a purplish tinge. However the oxidation process can be accelerated by application of heat as in Unna's method. (G. Gurr, 1963 p. 88 & 91); also E. Gurr, 1960, pp. 264-268).

Loeffler's methylene blue:

      Methylene blue       0.5 g
      1% w/v Aq. KOH    1.0 ml
      Ethanol                 30.0 ml
      D.water                70.0 ml
      Warm the water to 50 C., stir in methylene blue and add other ingredients, cool and filter before use.

    Polychrome methylene blue (Unna):

      Methylene blue     1.0 g
      Pot. carbonate     1.0 g
      Ethanol                20.0 ml
      D.water               100 ml
      Dissolve methylene blue in water, add pot. carb. and alcohol, place in boiling water bath and evaporate to 100 ml.

Any other polychrome methylene blue formulation should work well also.

Results: Bacilli appear Navy Blue with Anthax showing a narrow area (capsule) around and between bacilli that is reddish purple (metachromatic). A strong word of warning: many species of bacillus may also be encapsulated, e.g. Cereus etc. If you produce any positives get them confirmed at a Reference Microbiology Lab. for Infectious Diseases, or try the Armed Forces Institite of Pathology.

Gurr doesn't give any further references in his book as to McFadyean, whether the method was published or by personal communication.


"Encyclopedia of microscopic stains," by Edward Gurr. London: Arnold, 1960. (pp 264-268)
"Biological Staining Methods." by George T. Gurr. 7th Edition. 1963. (Published by George T. Gurr Ltd. 136-144, New King's Road, London, S.W.6.)

Mike Rentsch
Australian Biostain P/L
Ian Montgomery
Bryan Hewlett