Aluminum v blocksizes

Now, in Nature, Dr. Landrum B. Shettles, of Columbia University's College of Physicians and Surgeons, reports on what may be a simple way to differentiate X from Y. In his laboratory Shettles spread sperm cells thinly on a glass slide, allowed them to dry, and examined them with a phase-contrast microscope�a type that makes tiny objects look like bright halos of light against a dark background, showing up details that ordinary microscopes miss.