The staining mechanisms of Gomori's aldehyde-fuchsin are not
yet fully understood. It seemed therefore timely to review the history of
this dye class in context with current dye and aldehyde chemistry. In 1861
Lauth treated basic fuchsin with acetaldehyde. This dye became known
as Aldehyde Blue, but consisted of violet and blue dyes. Schiff (1866) studied
several aldehyde-fuchsins; these compounds contained two molecules of dye
and three molecules of aldehyde. Acetaldehyde-fuchsin prepared according
to Schiff's directions showed staining properties similar to those of Gomori's
aldehyde-fuchsin. This dye class was soon superseded by new dyes more
suitable for textile dyeing, and chemical investigations of aldehyde-fuchsins
ceased around the turn of the century. Gomori's aldehyde-fuchsin has been
regarded as a Schiff base. However, according to chemical data, low molecular
aliphatic aldehydes and aromatic amines tend to form condensation
products. Correlations of chemical and histochemical observations suggest
such processes during aging of dye solutions. Models of dimers and polymers
of aldehyde-fuchsin could be built without steric hindrance. The nature
of the bonds formed by various components of aldehyde-fuchsin solutions
is not clear. However, cystine in proteins, e.g. in basement membranes,
apparently does not play a role in the binding of aldehyde-fuchsin by unoxidized
Carnoy- or methacarn-fixed sections.