Yogurt. Dairy products, such as yogurt and milk, are one of the best sources of calcium.

Synapses. A synapse allows a neuron to pass an electrical or chemical signal to another cell.

Hematocrit. The normal range of red blood cells is 41-50% for men and 36-44% for women.

Christine "George" Jorgensen. In 1952, George Jorgensen became Christine Jorgensen after the world's first sex-change operation in Denmark.

Interferon. There are two different types of Interferon.

40 Percent. Going gray before 20 in Caucasians, or before 30 in African-Americans is considered premature graying.