There is hereby granted to and vested in the Michigan public utilities commission, hereinafter styled the “commission,” the power to control and regulate corporations, associations and persons engaged, directly or indirectly, in the business of purchasing or selling or transporting natural gas for public use; and said commission shall investigate any alleged neglect or violation of the laws of the state by any corporation, association or person purchasing or selling natural gas and transmitting or conveying the same by pipe line or lines for public use: Provided, That nothing in this act shall be construed to prevent oil and gas operators or producers of gas from laying pipe lines to transport or transmit gas to drilling wells within this state: And provided further, That factories or industries in this state may transport or transmit gas through pipe lines for their own use in plants located wholly within this state without constituting themselves a common purchaser within the terms of this act.