The staining of bacterial capsules and slime with ferric compounds.

In 1946 Hale described a method for demonstrating acid mucopolysaccharides in sections based on the affinity of these compounds for colloidal iron oxide in acid solution. The combined iron was demonstrated by conversion to prussian blue. It has been found that bacterial capsules and slime are very well stained by Hale's method. This is possibly due to their content of acid mucopolysaccharides, but this is not certain, since doubts have been cast on the specificity of this reaction (Pearse, 1953). The method of Rinehart and Abul-Haj (1951) is also applicable, but the iron solution is troublesome to prepare and the results are no better than with Hale's method. The following technique is based on Hale's method, but saccharated iron oxide is used, resulting in considerably deeper staining.