In all cities of the third class in this state there is hereby created and established, at the option of the mayor and common council of any such city, a board which shall be styled “The Social Welfare Board of the City of ______”. All powers and duties connected with and incident to the relief and prevention of dependency, relief and care of the indigent, and the care of sick dependents, with the exception of the insane and those suffering with contagious, infectious and transmissible diseases, and excepting those persons who may be admitted to the county poorhouses of the counties in which such cities are located, shall be exclusively invested in and exercised by the board. The board shall have power to receive and expend donations for social welfare purposes, and shall have exclusive control of the distribution and expenditure of any public funds set aside and appropriated by such cities for relief of the temporary dependent. The board shall have power to sue and be sued, complain and defend in all courts, to assume the care of or take by gift, grant, devise, bequest or otherwise, any money, real estate, personal property, right of property or other valuable things, and may use, enjoy, control, sell or convey the same for charitable purposes, to have and to use a common seal and alter the same at pleasure. The board may make bylaws for its own guidance, rules and regulations for the government of its agents, servants and employees, and for the distribution of the funds under its control.