摘录

Chapter One THE INNER UNIVERSE "The most beautiful thing we can experience is the mysterious. It is the source of all true art and science." --Albert Einstein While astronomers continue to produce amazing pictures of outer space, biology researchers in the labs are opening an equivalent view of the cosmos that lies within. Traveling through the farthest reaches of inner space, they are capturing pictures no less spectacular in form and content. Their different methods of imaging, at depths of intimacy almost impossible to comprehend, are yielding a kaleidoscopic variety of "inside information" about ourselves; and now, for the first time, many of the most basic biological processes can be illustrated with photographs and images rather than described with abstract formulas and diagrams. As more of us come to realize that these "biovisions" are profoundly personal, with relevance and direct usefulness for our individual lives, their claim on our attention will necessarily grow and permeate our collective consciousness. We are finally learning to recognize--and harness for our own benefit--the mysterious, beautiful, treacherous, miraculous forces of the inner universe.     From its inception the camera has captured our varied but common human experience, as well as the world around us, with indelible images. Some pictures have become visual symbols of historical events, even of whole eras, by evoking their look and feel and meaning through a single snapshot. Now some of the most important pictures are being taken by biomedical scientists, who use increasingly accurate "cameras" to see the otherwise unseen. To say they are making visual expeditions into the human body is an understatement. They are peering into our living cells, of which our bodies are composed in the first place, and opening vistas within the single cell's nucleus. Here in the realm of the infinitely small, researchers have discovered yet another vast landscape, containing the trail of chromosomes with their molecular strands of DNA, which include our genes. They are bringing back startling new snapshots of life itself.     The new visual techniques, along with creative ways of developing and using them, provide the foundation for seeing our future selves. Nearly all biological scientists act as photographers. Their technologies vary from light or electron microscopes to computer visualization, but each researcher probes for visual information which, in turn, contains scientific truth. The very act of seeing , one way or another, is inseparable from the science itself. As the ability to see becomes increasingly sophisticated, the knowledge advances.     Dr. Nancy Kedersha's goal as a biologist is to define, differentiate and make legible the microscopic components of tissues and cells of body or brain. She uses a technique with a specially equipped light microscope called immunofluorescence, whereby antibodies (protein molecules) of the immune system are used to carry dye to different tissues or cells. When the antibodies attach themselves, specific cell structures seen under certain wavelengths of light become illuminated according to the dye's color.     In the early part of the twentieth century, scientists made a great leap from examining bones to looking into the organs with X-rays, but in the final three decades of the century the X-ray and the computer converged in the form of Computerized Axial Tomography (CAT or CT), which produces "cross-section" images revealing the actual substance of the living body and brain. This technology sends beams through the body to an array of detectors which, in turn, send signals to a computer that translates the signals into pixels on a video monitor. The essential factor is the computer, which can enhance the image by coloring and enlarging it.     The assigning of specific colors to different aspects of biological images took a dramatic turn when Dr. Robert Ledley, inventor in 1974 of the first "all-body" CAT scanning technology, rendered his earliest images of the brain and body in different colors.     "I used color as a means of clarity and differentiation," Dr. Ledley said, "in order to help scientists and surgeons and other doctors see small deviations. It was my opinion that the color would serve a very useful function, which I still believe. After I sold the patent for commercial use, however, the company marketed a product that would create only black-and-white images. Why? Because sales people thought CAT scans would seem more `scientific' that way. But let me ask you: How many different shades of gray can you really see?"     Accompanying the molecular explorers are modern cartographers who map our minds in ways that have become possible only now. The journal Science has even called fine current era of neuroscience the "Age of Imaging." An area of the brain under its cortical surface, for example, is the, cingulate gyrus, which begins at the pre-frontal region (involved in planning for the future) and extends all the way back to the sensory areas (which play a crucial role in a person's attentiveness and mood). Medications enhancing the metabolism of the cingulate gyrus can treat the sadness of depression and even lift a person's spirits.     "If there is a brain area for hope," said Dr. Monte Buchsbaum of Mount Sinai School of Medicine in New York, "this is certainly a candidate."     PET cameras record changes in the brain's chemistry, with fluctuating thoughts and even emotions resulting in different images. The technology operates on the principle that blood is rushed to busy areas of the brain, delivering oxygen and nutrients to the neurons. Patients are injected with radioactive glucose, then scanned for the rays emitted as the solution metabolizes. The scans, revealing heightened neuronal activity, indicate which areas of the brain are sent into motion when different parts of fine body are used.     Magnetic Resonance Imaging (MRI) offers a detailed picture of the brain's structure, so researchers can focus on specific regions. The MRI camera produces images by subjecting the patient's head to a strong magnetic field, followed by several pulses of radio waves. Images of the brain's structure, generated and colorized by computer, appear on a video monitor.     PET and MRI technologies were combined to produce Dr. Buchsbaum's view of the cingulate gyrus rendered three-dimensionally by computer graphics. Such devices, one way or another, function as cameras, and the brain researchers using them behave as photographers. In doing so they make creative decisions or interpretations to further their "seeing" of human consciousness at its core. The neuroscientists may not be artists, but, indeed, there is an art to what they do.     Visual information about the active human brain includes moment-to-moment images of its blood flow, chemical activity and electrical signals. Neurologists can witness and record not just this amazing organ's structure but its function and behavior. They can watch what takes place among billions of neurons amid trillions of connections as we perform motor activities, exercise thinking powers, summon memories and speak languages. Researchers can even look at the brain's role in the experience of joy or sadness, fear or anger. At the same time, they can observe what happens among the neurons when things go wrong and produce forms of mental illness or brain-related maladies.     Researchers have found that the activities of cells and neural networks are tied both to the instructions of our genes and to the effects of environment or life-style. Instead of debating any longer over whether we are "born" one way or another, today's biologists foresee a time when we will know how much of a person's behavior is due to genetics and how much results from experience. It appears that the more we learn about what nature has given us, the greater is the wisdom we gain about what to do for ourselves and our children in terms of nurture.     The perceptual adventure that began more than a century ago with X-ray pictures of our anatomy has taken a sharp, deep turn into each of our microscopic cells and through their inner core, the nucleus, to the genetic code of our inheritance. Within this record of our evolutionary past is also the basic blueprint for our individual lives. Looking at some of the pictures being made along the way, we can begin to perceive our future selves.     The union of two cells, egg and sperm, produces a genetically identical cell line throughout developement with chromosomes from each parent. The molecular DNA of the chromosomes is exactly the same in each cell, but, nevertheless, different cells eventually respond to distinct segments of the DNA--that is, to separate sets of genetic instructions--to produce their own unique proteins. In this way the multiplying cells begin to differentiate until the complete human organism constitutes about 200 different kinds of cells with varying shapes, sizes and roles to play. The cells of an adult will number up to 100 trillion altogether, composing all skin and blood and bones and organs. Of these cells, working as members of a vast organization, about 100 billion become the neurons necessary for functioning of the brain. The latter will communicate with each other, and with the rest of the body, through about 500 trillion connections.     Dr. Michael Tucker photographed a four-cell human embryo in vitro ("in glass") at 400X magnification and transformed it into a color-enhanced 3D image. The "test tube baby" was produced by fertilizing an egg in a dish before transfer into the prospective mother's uterus. This method was used for a couple unable to conceive because the husband had very few sperm. After single-sperm injection, the successful union of the father's sperm and the mother's egg resulted in an embryo with chromosomes contributed from each parent. During the second day, the one-cell embryo divided twice and multiplied to make four cells; on the third day, each of the four will double to make eight.     From fertilization onward, each of the embryo's cells contains all forty-six of the necessary human chromosomes that carry all of the genes of a future self. Our lives are basically composed of many specific cells, all working in their different and specific ways. Although the sizes of different cells vary widely, their general dimensions are difficult to comprehend. You would need to line up 2,500 kidney cells in a row to cover the length of one inch, but kidney cells are rather large in comparison to red blood cells--ten times larger. That is, you would need 25,000 red cells (corpuscles) to span the same inch. About 250 average-size human cells could rest together within the period at the end of this sentence.     During their formation in bone marrow, red blood cells lose their nuclei. They contain the protein complex hemoglobin, which gives blood its red color. Hemoglobin also picks up oxygen in the lungs and releases it to cells and tissues throughout the body. In a life span of about 120 days, one red blood cell travels more than 900 miles through the circulatory system before breaking apart, usually in the liver. New red cells are constantly produced to carry more shipments of oxygen where needed.     Dee Breger, an artist who works in the world of science, pays simultaneous attention to the needs of researchers and to the dictates of her aesthetic values. "Scanning electron imagery is the only way we can see ultramicroscopic objects as they really exist," she said. "In using this technology, my goal is to reveal a picture of the microworld that inspires a sense of wonder at its diversity, astonishment at its elegance and delight in the stories it has to tell. As an observer trained in the diverse fields of art and microscopy, I want my images to not only stir the imagination with their compositions and content but also to represent the highest achievements in technical operation of the electron microscope, darkroom techniques and color renderings of the original black-and-white micrographs. Grounded in science, I respect the integrity--the truth--of the specimens and want my images to be as informative as they are arresting. As an artist, I want them to be more beautiful than necessary."     New methods of visualization are yielding images of the smallest structures and processes of human life. Understanding its fundamental unit, the living cell, is essential to learning how we function in health and how abnormal processes lead to disease. Why and how do cells divide? How can they "recognize" other cells and even "communicate" with them? Why do some cells die (as often they should) while others continue to multiply (as often they should not)?     Human life is based on the lives of many individual cells, and disease is the result of processes that go wrong within or among cells. Each of our trillions of cells contains a complete universe of its own, comprised of many smaller organs (organelles) with distinctly different forms and functions. Included are several thousand types of protein molecules, structural or functional, and hundreds of different kinds of enzymes that help chemical processes needed by the body.     Scientists can watch this activity of components to learn how cells work together and how each cell's elaborate inner mechanisms operate. Copyright © 1998 Camera Works, Inc.. All rights reserved.