hich was regarded as a "law"
of the United States;[688] the release of an election official held
under State authority for perjury on the ground that jurisdiction to
punish a false witness belonged to the federal courts in this
instance;[689] and the release of a collector of internal revenue held
in Kentucky for his refusal to file copies of his official papers with a
State court.[690] Similarly, the governor of a national home for
disabled soldiers was released from Ohio custody for serving
oleomargarine in the home in violation of an Ohio statute.[691] A more
extreme exercise of _habeas corpus_ jurisdiction is illustrated by
Hunter _v._ Wood[692] where a ticket agent of a railroad held in State
custody for an overcharge on a ticket was released because prior to his
trial in the State court, a United States circuit court had enjoined the
enforcement of the statute. The element common to all of these cases is
the supremacy of the National Government and the inability of the States
through judicial proceedings or otherwise to obstruct the enforcement of
federal authority. The doctrine of comity is inapplicable in this
category of cases.

COMITY AS A PRINCIPLE OF STATUTORY CONSTRUCTION

On the other hand, in Ex parte Royall,[693] decided in 1886, the Court
held that the jurisdiction of the lower federal courts in the above
category of cases involved no duty to release persons from State custody
but only a discretion to do so. Such discretion, the Court declared,
"should be exercised in the light of the relations existing, under our
system of government, between the judicial tribunals of the Union and of
the States, and in recognition of the fact that the public good requires
that those relations be not disturbed by unnecessary conflict between
the courts equally bound to guard and protect rights secured by the
Constitution."[694] In pursuance of these principles the Court has
subsequently formulated rules to the effect that mere error in the
prosecution and trial of a suit cannot confer jurisdiction upon a
federal court to review the proceedings upon a writ of _habeas
corpus_;[695] that the writ of _habeas corpus_ cannot be substituted for
the writ of error, however serious the errors committed by the State
court;[696] that except in extreme and urgent cases the federal courts
will not discharge a prisoner in State custody prior to final
disposition of the case in the State courts, where the prisoner must
first exhau