Question.

Why does alkaline Congo red stain amyloid feebly in sections of some specimens but not others?

Answer.

Here is one possibility. In developing the alkaline Congo red method, Dr. Holde Puchlter noticed decreased staining with prolonged fixation in formalin or NBF.  This decrease even applied to unstained sections stored under conditions where formaldehyde was present in the ambient air.

Susan Meloan
Medical College of Georgia, Augusta
(smeloan[AT]mail.mcg.edu)