The leng: h of adverse possession necessary to give title varies greatly under the statutes of the several states. In a few states an absolute limit is fixed, beyond which mental unsoundness will not prevent the acquisition of title.517 So a few states have an ultimate limit, beyond which neither exceptions nor disabilities can save the right of action,518 In many of the states a possession based either on color of title, or upon a title which is defective only in some named particular, or on a mode of conveyance which it is the policy of the law to favor, is protected against the entry or suit of the dispossessed owner after a much shorter period than that which bars the right against a naked possession.519