Columbia subject headings:
Medicine--Specialties and specialists--Directories.
Physicians--Canada--Directories.
Physicians--United States--Directories.
Harvard subject headings:
Medicine--Specialties and specialists--Directories.
Physicians--Canada--Directories.
Physicians--United States--Directories
Princeton subject headings:
Directories.
Medicine--Specialties and specialists--Directories.
Physicians--Canada--Directories.
Physicians--United States--Directories.