orted therein and of those
who are employed in such transportation, no matter what may be the
source of the dangers which threaten it. That is to say, it is no
objection to such an exertion of this power that the dangers intended to
be avoided arise, in whole or in part, out of matters connected with
intrastate commerce."[401]

Four years later the Hours of Service Act of 1907[402] was passed,
requiring, as a safety measure, that carriers engaged in the
transportation of passengers or property by railroad in interstate or
foreign commerce should not work their employees for longer periods than
those prescribed by the Act. In sustaining this legislation the Court,
speaking through Justice Hughes, said: "The fundamental question here is
whether a restriction upon the hours of labor of employes who are
connected with the movement of trains in interstate transportation is
comprehended within this sphere of authorized legislation. This question
admits of but one answer. The length of hours of service has direct
relation to the efficiency of the human agencies upon which protection
of life and property necessarily depends. * * * In its power suitably to
provide for the safety of the employes and travelers, Congress was not
limited to the enactment of laws relating to mechanical appliances, but
it was also competent to consider, and to endeavor to reduce, the
dangers incident to the strain of excessive hours of duty on the part of
engineers, conductors, train dispatchers, telegraphers, and other
persons embraced within the class defined by the act."[403]

But by far the most notable of these safety measures were the Federal
Employers Liability Acts of 1906 and 1908,[404] the second of which
merely reenacted the first with certain "unconstitutional" features
eliminated. What the amended act does, in short, is to modify, in the
case of injuries incurred by the employees of interstate carriers while
engaged in interstate commerce, the defenses that had hitherto been
available to the carriers at common law. The principal argument against
the acts was that the commerce clause afforded no basis for an attempt
to regulate the relation of master and servant, which had heretofore in
all cases fallen to the reserved powers of the States; that indeed the
rules of common law modified or abrogated by the act existed solely
under State authority, and had always been enforced, in the main, in the
courts of the States.[405] Countering this a