The microscope has undergone enormous changes since its invention centuries ago. Once considered "flea glasses" suitable only to amuse wealthy dabblers in science, the microscope is now an indispensable research tool in many fields-including medicine. Without it, entire fields of medical research and practice would be impossible. Even everyday medical procedures such as diagnosing diseases rely on microscopes. If cancer is suspected, for example, symptoms are only uncertain guides; a microscopic examination remains the only sure way to confirm or disprove the presence of cancerous cells.

Meanwhile, new forms of microscopy, holding out the promise of further advances, are being developed all the time. It is doubtful that any single one of these will serve all the needs of medical science in the future, however. Each type of microscope and technique provides different and distinct forms of data. Chances are...