The second was specifically
rejected in McKane _v._ Durston;[138] the third, in Detroit _v._
Osborne.[139] The fourth has become a settled doctrine of Constitutional
Law.[140] In the words of Justice Miller in the Slaughter-House
Cases,[141] the sole purpose of the comity clause was "to declare to the
several States, that whatever these rights, as you grant or establish
them to your own citizens, or as you limit or qualify, or impose
restrictions on their exercise, the same, neither more nor less, shall
be the measure of the rights of citizens of other States within your
jurisdiction."[142] It follows that this section has no application in
controversies between a State and its own citizens.[143] It is deemed to
be infringed by a hostile discrimination against all nonresidents[144]
but not by such differences of treatment between residents and
nonresidents as the nature of the subject matter makes reasonable.[145]

HOW IMPLEMENTED

This clause is self-executory, that is to say, its enforcement is
dependent upon the judicial process. It does not authorize penal
legislation by Congress. Federal statutes prohibiting conspiracies to
deprive any person of rights or privileges secured by State laws,[146]
or punishing infractions by individuals of the right of citizens to
reside peacefully in the several States, and to have free ingress into
and egress from such States,[147] have been held void.

CITIZENS OF EACH STATE

A question much mooted before the Civil War was whether the term could
be held to include free Negroes. In the Dred Scott Case,[148] the Court
answered it in the negative. "Citizens of each State," Chief Justice
Taney argued, meant citizens of the United States as understood at the
time the Constitution was adopted, and Negroes were not then regarded as
capable of citizenship. The only category of national citizenship added
under the Constitution comprised aliens, naturalized in accordance with
acts of Congress.[149] In dissent, Justice Curtis not only denied the
Chief Justice's assertion that there were no Negro citizens of States in
1789, but further argued that while Congress alone could determine what
classes of aliens should be naturalized, the several States retained the
right to extend citizenship to classes of persons born within their
borders who had not previously enjoyed citizenship, and that one upon
whom State citizenship was thus conferred became a citizen of the State
in the full sense of