“Because good fixative, paraffin embedding, microtome and eosin stain
were not available prior to the 1860s, pioneer microscopic pathologists
most often obtained their specimens for microscopic examination by
scraping and teasing out the cut-surface of tissues or by preparing smears
from fluids and aspirates.”^13 Little wonder that the first breakthrough
observations of the 1830s and 1840s would be achieved when sampling
blood and skin.
With the German openness to dyestuffs and chemical experimentation,
it was natural that microscopists would start to tinker with tissue dyes.
Scientists were used to altering chemical protocols in order to achieve
better color penetration and colorfastness in cloth, and it was only a matter
of time until the right recipe would be determined for medical use. There
were essentially no worthwhile stains for microscopic slides until the
decade after Perkin’s discovery, and it was another South American plant
that garnered attention. The logwood tree, Hematoxylon campechianum, is
an indigenous tree of the New World whose roots and trunk exude a ruddy
turbid colorant when boiled or steamed,^14 and was used for centuries as a
dye for cotton. The Spanish used the dye (as did the Mayans), and also
American soldiers during the Civil War.
A century and a half ago, hematoxylin was identified as a potent
mammalian tissue stain, causing a bland, colorless tissue sample to adopt
a deep purple, india ink–like hue. Experimentation with various chemicals
added to hematoxylin yielded a combination that readily stained the inner
parts of the cell, later revealed to be the nucleus, where the chromatin
(DNA and RNA) is housed. A decade later eosin, a reddish-pink dye, was
discovered as another dye that readily attached to other cellular structures,
yielding a fuchsia shade over the entire representation. While the newly
discovered dyes provided much improved visualization of the material, it
was like looking at a coloring book pigmented with only one crayon.
Washing the slide material with alcohol and other drying agents led to
visual changes in the tissues, and a scientific game of hide-and-seek
transpired as the German histologists played with the sequence and timing
of chemical exposure. A double-staining technique using two stains in
succession, and, finally, the combination of hematoxylin and eosin in 1876
set the standard that is still used everywhere today.^15
The combination of hematoxylin & eosin (H&E), with almost three
million slides per day prepared in the cytopathology labs around the