Nothing in this subchapter shall be construed as restricting the respective States from enforcing any and all statutes enacted for police regulation, nor shall the police power of the respective States be, by this subchapter, impaired or restricted, and all laws heretofore enacted by the respective States or any thereof, or that may hereafter be enacted as regards public health or public welfare, shall at all times be in full force and effect: Provided, however, That nothing in this section shall be construed as limiting or restricting the power and authority of the United States.