Civil Code, Art. 1556

Should the vendee lose, by reason of the eviction, a part of the thing sold of such importance, in relation to the whole, that he would not have bought it without said part, he may demand the rescission of the contract; but with the obligation to return the thing without other encumbrances that those which it had when he acquired it. He may exercise this right of action, instead of enforcing the vendor's liability for eviction. The same rule shall be observed when two or more things have been jointly sold for a lump sum, or for a separate price for each of them, if it should clearly appear that the vendee would not have purchased one without the other. (1479a)