Columbia subject headings:
Einthoven, Willem, 1860-1927--Correspondence.
Lewis, Thomas, Sir, 1881-1945--Correspondence.
Harvard subject headings:
Cardiology--Biography.
Cardiology--Correspondence.
Einthoven, Willem, 1860-1927
Electrocardiography--Biography.
Electrocardiography--Correspondence.
Lewis, Thomas, 1881-1945.
Lewis, Thomas, Sir, 1881-1945
Princeton subject headings: