Well-defined dark figures stand out against a backdrop of soft pink and salmon hues suggestive of a tropical sunset. What mental picture does that create for you? Does it sound like art or science? Perhaps you are imagining a photograph from a memorable vacation, or a painting of a vibrant landscape. Of all the mental pictures created, I bet you didn’t think I was describing a stained tissue sample that was “painted” using carefully balanced chemistry! Normally, these figures would go unseen to the naked eye. What are they, how do they make their debut, and what role do they play in diagnostics?
These questions will be answered as we take a brief tour of the Histology Laboratory in the Wildlife Disease Labs, one of the multidisciplinary diagnostic and research facets of the San Diego Zoo Institute for Conservation Research. I often refer to histology as the arts and crafts lab in which I am the histology technician/resident artist! Here, I am honored to practice the creative work required to transform representative samples of animal tissue into diagnostic microscope slides. Imagine this is much like the painter who carefully selects choice color from a palette for application to a pale, uncommitted canvas.
Preparatory work must be done to set the stage for the defining stain that will make the unseen figures in the tissue come to life. The process is rather simple yet delicate, requiring precision for specific tissue element demonstration. To start, select tissue samples are chemically processed to prevent their decomposition and to create within the soft structures a paraffin scaffold. Once processing is thoroughly completed, the tissue samples are embedded in paraffin to form a block. The block is then carefully trimmed with a cutting instrument to create thin, delicate, and colorless sections no thicker than a human hair. These thin sections are then floated on a heated water bath and adhered onto glass microscope slides. All this is done to prepare the perfect canvas on which I will display my work.
For the demonstration of the “dark figures,” I apply the gold standard screening stain. It is called the hematoxylin and eosin stain, or most frequently referred to as the H&E. In the initial part of the staining process, a hematoxylin dye solution is used to form basophilic bonds with the cryptic nuclei of the cells, causing them to appear dark purple. As the stain process continues, the remaining unstained features are washed with an eosin dye solution. On completion, the H&E stain results reveal dark purple staining nuclei highlighted against surrounding tissue architecture visible in various shades of pink.
When all is finished, I review my work. I still cannot help but marvel at the beauty of detail, the intricacies of design, and the uniqueness of the features of the tissue structures displayed on the slides. If I see that the work is good, the H&E-stained slides will be delivered to our staff pathologists, who will translate the diagnostics meaning of the dark purple staining figures on the glass slides. The features of the nuclear bodies reflect many of the dynamic processes occurring within the tissue such as injury, cell death, or disease. This validates the importance of the H&E to the pathologists, whose diagnostic translation insures the health of our animal collection.
So, I ask again: does it sound like art or science?
Yvonne Cates, H.T., ASCP, is a research coordinator with the San Diego Zoo Institute for Conservation Research.