Isabella Beukes, of Santa Rosa, Calif., has been legally blind for more than 40 years. An experimental treatment derived from embryonic stem cells seems to have enabled her now to see not just color but also some shapes. Tim Hussin for NPR hide caption

itoggle caption Tim Hussin for NPR

Insulin is produced by the green cells that are in clusters about the same size as the islets in the human pancreas. The red cells are producing another metabolic hormone, glucagon, that prevents low blood sugar. Harvard University hide caption

itoggle caption Harvard University