It has been estimated that it was not until the early 20th century that going to the doctor for an internal ailment produced more good than harm.  A large part of medical progress in the first half of the 20th century was due to advances in our knowledge on a molecular level of the human body, its disorders, and possible treatments.  These four sessions will look at the discovery of vitamin A (the first vitamin discovered), insulin (for the treatment of diabetes), penicillin (the first mass-produced antibiotic), and chlorpromazine (which ushered in modern psychopharmacology).