DIGITAL ANALYTICAL HISTOLOGY: AN OVERVIEW
Histology (histo, Gr. - "tissues"; ology, Gr. - "study of") is largely an exercise in pattern recognition. Here, you are asked to learn, and then apply, a number of simple rules to images seen with the use of a light or an electron microscope. This will help you recognize, understand, and interpret images in their contexts as the cells, tissues, organs, and organ systems of the human body. When the rules are understood and applied correctly, the function of the biological materials of origin are also understood with much greater clarity than if the learning process is approached merely as an exercise in memorization.
The Digital Analytical Histology (DAH) interface is organized in the same manner as a histology textbook: namely, into chapters that reflect the way histology has been conceptualized for the past century. Each image is annotated with transparent overlays that illustrate important, basic histological features. In addition, many images have labels that highlight specific tissues, organ regions, or other notable features. Each physical slide is the basis for a set of images, which lead from the lowest to higher magnifications through a series of "hotspots." These hotspot areas have been identified by expert histologists as significant, so students learn to view the images "through expert eyes."
We emphasize that DAH cannot be used successfully in isolation. It is essential that all students of histology attend the relevant lectures and study a recommended standard histology textbook in order to acquire a good foundation in this discipline. We advise you to keep a histology textbook next to your computer while you use DAH, so the basic explanatory information, diagrams, and micrographs are available as a ready reference.USING THE DAH WEB SITE
This Web site is to be seen as a metaphor for using a microscope. The first image of each slide (specimen) is a low-magnification view of the whole section, approximating the view that one would have with the naked eye or with a 5-10X hand lens. Clicking on the microscope icon in the upper-left-hand corner of the screen "turns a lamp on" and displays one or more rectangles that represent a higher magnification of the current image. The level of magnification is displayed in the upper-left-hand corner of each image; the Northwestern University seal is usually displayed in the upper-right-hand corner.
As you move to higher magnification of an image, a series of thumbnails of the images is seen vertically along the left-hand side of the screen; the thumbnails will reflect your travels through magnifications. The specific area you just left is indicated by a bright blue (cyan) box inside the thumbnail. The thumbnail sketches themselves are active parts of the screen; when you click on any of them you return to its full-size, lower-magnification image. This capability mimics the way one uses an actual microscope, jumping easily from a high-to a low-magnification view by selecting a different objective on the microscope.
One of the key concepts in understanding histology is that there are four basic tissue types: epithelial tissue, connective tissue, muscle tissue, and nerve tissue. With very few exceptions, all organs contain all four of these basic tissues. However, sometimes only two or three of the basic tissues can be discerned at the light-microscopic level. To assist you, virtually all the images you will see on the Web site have a set of "tissue buttons," which will allow you to highlight those types of tissues that can be recognized in a given image.
If you pass the computer mouse over one of the four tissue buttons (Epi, CT, Mus, or Ner), that button will "glow" if that particular type of tissue is present and recognizable in the specimen. Clicking on a tissue button will highlight the tissue itself with a transparent, colored overlay. The button names and colors conform to the way anatomical drawings are presented in anatomy textbooks: Epi=blue, CT=green, Mus=red, and Ner=yellow. An overlay appears on the screen only as long as the mouse hovers over its tissue button.
Buttons labeled "Labels", "Organ Terms", and "Specific Tissues" appear across the top of the screen. When they are "active" (available for use), they have a black "glow"; and when additional information is available, a pull-down list appears to their right. To view the image with features associated with the image on the screen, select the appropriate item from the pull-down list. These images disappear from the screen when the user clicks on any of the active basic tissue types.
The "Notes" button makes additional features available. This button can be activated by clicking with the mouse, but only if it "glows" when the mouse passes over it. Clicking on the forward and backward arrows in the lower-left-hand corner of the palate will allow you to move to other specimens in the chapter being studied. A list of all the specimens in the chapter can be seen, and individually selected from a pull-down menu, by clicking on the "Other Slides" button in the lower-right-hand corner of the palate.
Clicking on the "Search" button enables the learner to search the Web site by chapter, from a list of keywords, or by a "wildcard" choice. The results of a search are represented by a thumbnail of the image, which contains the word or term that the user entered. When the thumbnail is clicked on, that specific place in the site appears on the screen. The user may then go on to explore other images, labels, overlays, etc., in the context of the search results.
We have included a brief demonstration of how to use the Web site that can be accessed from the opening screen of DAH. In order to use it properly, you need to have the latest version of the "Flash Player" on your computer. This software can be downloaded over the Web from Macromedia.com. Once downloaded, it is easily installed as part of your Internet Explorer browser.
TECHNICAL COMMENTS
The majority of the slides used on this Web site are from the collection of microscope slides used in the Medical Histology component of "Structure-Function," a basic science course for first-year medical students at Northwestern University Medical School.
Most specimens are 20-30 µm paraffin sections prepared in the period from 1920-1960 under the direction of Leslie B. Arey, Ph.D., in the Department of Anatomy at Northwestern University Medical School. He joined our faculty in 1917 and remained an active faculty member for 73 years, until he passed away in 1988 at the age of 97. Dr. Arey was internationally known as a pre-eminent scholar in the fields of histology and human embryology. He served as Chairman of our Department of Anatomy from 1927 until 1954, and during that time he built the collection of microscope slides that we still use for our medical students today. Other slides in this collection are commercial preparations of paraffin sections, and some are 1.5 µm plastic sections.
Many of the materials Dr. Arey used were from normal human tissue or from primates. Such materials are no longer readily available because of changes in the way such tissue is gathered today. DAH will provide a way to preserve his irreplaceable slide collection in an enduring, high-quality, digital format. This will make it possible for future generations of students to continue to study and learn from these exceptional slides.Each of Dr. Arey's "special" slides used on the DAH Web site will be identified with this symbol:
The majority of the DAH specimens were stained with Hematoxlin-Eosin, or the Masson or Mallory trichrome stains commonly used for highlighting connective tissue components. Many other stains were used to help demonstrate certain components or characteristics of a specimen. For example, Wright's stain or Giemsa's stain were used for blood or bone marrow; reticular or elastin stains for reticular fibers or elastin fibers; PAS stain for highlighting basement membranes or other glycoproten-rich materials. It is not the purpose of this learning tool to have students learn to identify any particular stain. The student should bear in mind that colored stains are used only to provide visual contrast to the thin sections used in light microscopy. Except in a few special cases, color, per se, does not characterize any particular component of a specimen.
These images were captured using a Zeiss Axioskop 2 microscope equipped with Neofluar objectives of the following magnifications: 1.25X, 2.5X, 5X, 10X, 20X, 40X, and 63X. A Zeiss ProGres 3 digital CCD camera connected to a 0.4-2.0X zoom attachment was used to acquire the images. Zeiss Axiovision software was used to "grab" the images, and with minimal enhancement, the colored overlays and labeling of images was done using Adobe Photoshop® 6.01 and Adobe Image Ready® 3.
We developed the program to run on a Macintosh, or on a PC (Windows) platform using Internet Explorer, version 5 or higher. It is intended to be used on a 17" monitor set at a resolution of 800 X 600 or greater, and to "thousands of colors" on a Macintosh or on an IBM-compatible computer. DAH will run with smaller-size monitors, but scrolling will probably become necessary. It is possible to use DAH over a 56K modem, but we recommend a higher-speed Internet connection (DSL or cable modem), or, best of all, a direct Internet connection, such as would be available in your medical school library.
