against a revenue officer of the United States on account of any act
done under color of his office.[35] In the celebrated case of Cunningham
_v._ Neagle,[36] a United States marshal who, while assigned to protect
Justice Field, killed the man who had been threatening the life of the
latter, was charged with murder by the State of California. Invoking the
supremacy clause, the Supreme Court held that a person could not be
guilty of a crime under State law for doing what it was his duty to do
as an officer of the United States.

EFFECT OF LAWS PASSED BY STATES IN INSURRECTION

Since the efforts of States to depart from the Union, if successful,
would have been _pro tanto_ a destruction of the Constitution,[37] the
ordinances of secession adopted by the Confederate States,[38] and all
acts of legislation intended to give effect to such ordinances,[39] were
treated as absolute nullities. The obligation of every State, as a
member of the Union, and the obligation of every citizen of the State,
as a citizen of the United States, remained perfect and unimpaired.[40]
But acts necessary to peace and good order among citizens, such, for
example, as acts sanctioning and protecting marriage and domestic
relations, governing the course of descents, regulating the conveyance
of property, real and personal, and providing remedies for injuries to
person and estate, and other similar acts, which would be valid if
emanating from a lawful government, were regarded in general as valid
when proceeding from an actual, though unlawful government.[41]

The Doctrine of Tax Exemption

McCULLOCH _v._ MARYLAND

Five years after the decision in McCulloch _v._ Maryland that a State
may not tax an instrumentality of the Federal Government, the Court was
asked to and did reexamine the entire question in Osborn _v._ Bank of
the United States.[42] In that case counsel for the State of Ohio, whose
attempt to tax the Bank was challenged, put forward two arguments of
great importance. In the first place it was "contended, that, admitting
Congress to possess the power, this exemption ought to have been
expressly asserted in the act of incorporation; and, not being
expressed, ought not to be implied by the Court."[43] To which Marshall
replied that: "It is no unusual thing for an act of Congress to imply,
without expressing, this very exemption from state control, which is
said to be so objectionable in this instance."[44] Secondly the
appellan