60%. Obesity is caused by consuming more calories than are burned off.

Bilirubin. Bilirubin levels can be measured by blood tests.

Rib Cage. In an adult human, the rib cage has 24 bones and the hand 27 bones.

Using A Fluoride Toothpaste. Fluoride has been shown to help prevent cavities in teeth and was first added to a toothpaste in 1914.

Jonas Salk. The polio vaccine passed field tests and was first administered to the general public in 1955.

Butterfly. The thyroid is the largest endocrine gland in the body.