William R. Day,
Sligh v. Kirkwood — Opinion of the Court
“ That Congress has the exclusive power to regulate interstate commerce is beyond question, and when that authority is exerted by the state, even in the just exercise of the police power, it may not interfere with the supreme authority of Congress over the subject; while this is true, this court from the beginning has recognized that there may be legitimate action by the state in the matter of local regulation, which the state may take until Congress exercises its authority upon the subject. ”
