cts which have been regulated
by Congress, the primary task of the Court is to ascertain whether a
challenged State law is compatible with the policy expressed in the
federal statute. When Congress condemns an act as unlawful, the extent
and nature of the legal consequences of the condemnation are federal
questions, the answers to which are to be derived from the statute and
the policy which it has adopted. To the federal statute and policy,
conflicting State law and policy must yield.[14] But Congress in
enacting legislation within its constitutional authority will not be
deemed to have intended to strike down a State statute to protect the
health and safety of the public unless its purpose to do so is clearly
manifested.[15]

When the United States performs its functions directly, through its own
officers and employees, State police regulations clearly are
inapplicable. In reversing the conviction of the governor of a national
soldiers' home for serving oleomargarine in disregard of State law, the
Court said that the federal officer was not "subject to the jurisdiction
of the State in regard to those very matters of administration which are
thus approved by Federal authority."[16] An employee of the Post Office
Department is not required to submit to examination by State authorities
concerning his competence and to pay a license fee before performing his
official duty in driving a motor truck for transporting the mail.[17] To
Arizona's complaint, in a suit to enjoin the construction of Boulder
Dam, that her quasi-sovereignty would be invaded by the building of the
dam without first securing approval of the State engineer as required by
its laws, Justice Brandeis replied that, "if Congress has power to
authorize the construction of the dam and reservoir, Wilbur [Secretary
of the Interior] is under no obligation to submit the plans and
specifications to the State Engineer for approval."[18]

FEDERAL INSTRUMENTALITIES AND THE STATE POLICE POWER

Federal instrumentalities and agencies have never enjoyed the same
degree of immunity from State police regulation as from State taxation.
The Court has looked to the nature of each regulation to determine
whether it is compatible with the functions committed by Congress to the
federal agency. This problem has arisen most often with reference to the
applicability of State laws to the operation of national banks. Two
correlative propositions have governed the decisions in thes