No person shall be excused on any prosecution under the provisions of this Article from testifying touching anything done by himself or others contrary to the provisions thereof, but no discovery made by the witness upon such examination shall be used against him in any penal or criminal prosecution, and he shall be altogether pardoned of the offense so done or participated in by him. In all such prosecutions proof that the defendant was a party to a contract, as agent or principal, to sell and deliver any article, thing or property specified or named in this Article, or that he was the agent, directly or indirectly, of any party in making, furthering or effectuating the? same, or that he was the agent or officer of any corporation or association or person in making, furthering or effectuating the same,? and that the article, thing or property agreed to be sold and delivered was not actually delivered, and that settlement was made or agreed to be made upon the difference in value of said article, thing or property, shall constitute against such defendant prima facie evidence of guilt. Proof that any person, corporation or other association of persons, either as principal or agent, has established? an office or place where are posted or published from information received the fluctuating prices of grain, cotton, provisions, stocks, bonds and other commodities, or of any one or more of the same, shall? constitute prima facie evidence of being guilty of violating the provisions of this Article. (1905, c. 538, ss. 3, 4, 5; Rev., s. 3826; C.S., s. 2149.)