ACTS OF CONGRESS PROTECTIVE OF LABOR ENGAGED IN INTERSTATE TRANSPORTATION In the course of the years 1903 to 1908 Congress enacted a series of such measures which were notable both on account of their immediate purpose and as marking the entry of the National Government into the field of labor legislation. The Safety Appliance Act of 1893,[398] which applied only to cars and locomotives engaged in moving interstate traffic, was amended in 1903 to embrace "all trains, locomotives, tenders, cars," etc., "used on any railway engaged in interstate commerce * * * and to all other locomotives * * * cars," etc., "used in connection therewith."[399] In Southern Railway Company _v._ United States,[400] the validity of this extension of the act was challenged. The Court sustained the measure as being within Congress's power, saying: "* * * this is so, not because Congress possesses any power to regulate intrastate commerce as such, but because its power to regulate interstate commerce is plenary and competently may be exerted to secure the safety of the persons and property transported 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]