The party producing a writing as genuine which has been altered or appears to have been altered after its execution in a part material to the question in dispute must account for the appearance or alteration. He may show that the alteration was made by another, without his concurrence, or was made with the consent of the parties affected by it, or otherwise properly or innocently made or that the alteration did not change the meaning of the language of the instrument. If he does that, he may give the writing in evidence, but not otherwise.