We have the tendency to think of art and science as opposites. They can easily coexist; a good example is Leonardo da Vinci, who was as much of a scientist as he was an artist. In “Donate without Loss,” Kaviar Forge & Gallery features such scientific art (or artistic science) as medical drawings, anatomy and cellular structure. Plus, it’s an exhibition with a message: to raise awareness for the critical need for blood and bone marrow stem cell donations. Most people need to locate a matching donor outside of their family, with a 60 percent chance of finding one (for non-Caucasians, it’s 20 percent).