From and after the passage of this act, it shall not be lawful for any persons to carry on or work at the business of plumbing or house or building drainage in cities of the second, second class A, and third class of this Commonwealth until a certificate or license to engage in or work at said business shall have been granted said persons by the director of the department of public safety, or department or board or bureau of health, of such cities; nor until they have registered as such in the office of the department or board or bureau of health of said cities, as hereinafter provided.
53 P.S. § 4591