The corporation commission shall have full power to, and shall, prescribe just and reasonable classifications to be used and just and reasonable rates and charges to be made and collected, by public service corporations within the state for service rendered therein, and make reasonable rules, regulations, and orders, by which such corporations shall be governed in the transaction of business within the state, and may prescribe the forms of contracts and the systems of keeping accounts to be used by such corporations in transacting such business, and make and enforce reasonable rules, regulations, and orders for the convenience, comfort, and safety, and the preservation of the health, of the employees and patrons of such corporations; Provided, that incorporated cities and towns may be authorized by law to exercise supervision over public service corporations doing business therein, including the regulation of rates and charges to be made and collected by such corporations; Provided further, that classifications, rates, charges, rules, regulations, orders, and forms or systems prescribed or made by said corporation commission may from time to time be amended or repealed by such commission.