IMAGES PROVIDED BY:
1) Boston Globe / Contributor / Getty Images
2) MPI / Stringer / Getty Images
3) National Archives / Handout / Getty Images
4) Bettmann / Contributor / Getty Images
5) Hulton Archive / Stringer / Getty Images
6) Universal History Archive / Contributor / Getty Images
7) David Hume Kennerly / Contributor / Getty Images
8) PhotoQuest / Contributor / Getty Images
Arthritis Foundation: "Gout Causes."
Alzheimer's Association: "On Presidents' Day, Celebrate Reagan and Later Presidents' Actions to Move Alzheimer's Awareness Forward."
Library of Congress: "The Assassination of President Lincoln."
Mayo Clinic: "Addison's disease," "Alzheimer's disease."
Clinical Correlations: "Did Abraham Lincoln Have Marfan Syndrome?"
National Council for the Social Studies: "The Politics of Polio."
National Institutes of Health: "Multiple Endocrine Neoplasia," "Lead poisoning from retained bullets. Pathogenesis, diagnosis, and management."
National Park Service -- Franklin Delano Roosevelt Memorial: "Quotations."
New York Academy of Medicine: "The Secret Surgeries of Grover Cleveland."
NIH Medline Plus: "Medical Research Pays Off for All Americans: William Howard Taft -- Then & Now."
The Permanente Journal: "Early Detection of Colon Cancer -- The Kaiser Permanente Northwest 30-Year History: How Do We Measure Success?"
Reagan Library: "Text of letter written by President Ronald Reagan announcing he has Alzheimer's disease."
Skin Cancer Foundation: "Covert Ops: Skin Cancer Surgery in the Reagan White House."
University of Ottawa Faculty of Medicine: "JFK and Addison's Disease."
Yale School of Medicine: "MEN 2A and MEN 2B Syndrome."
University of Texas Health Leader: "Andrew Jackson."
University of Virginia Miller Center: "Grover Cleveland: Life After the Presidency."
University of Virginia -- Washington Papers: "George Washington's Terminal Illness: A Modern Medical Analysis of the Last Illness and Death of George Washington."