Rules for chemical formulas (Back to search) 1  Enter a sequence of element symbols followed by numbers to specify the amounts of desired elements (e.g., C6H6). 2  Use correct case for element symbols. 3  Elements may be in any order.  If only one of a given atom is desired, you may omit the number after the element symbol.
Half of all varicella zoster cases occur in children between the ages of 5 and 9. It has been estimated that, before the chickenpox vaccine was introduced in the U.S. in 1995, only 10 percent of Americans over the age of 15 had never had chickenpox.
I shall never have smallpox for I have had cowpox. I shall never have an ugly pockmarked face.. ... the annihilation of the smallpox, the most dreadful scourge of the human species, must be the final result .... It is hard to determine who invented vaccination. It may have been used in ancient times in China, India or Persia. But we do know that Edward Jenner was the first person which the first recorded vaccination in the western world.