This species of dementia is also frequently alleged and proved as a ground of impeach ing deeds. This particular form of mental disease may result either in total incompe tency, such as is produced by any form of insanity, or a greatly defective capacity, though short of total insanity, in which the court scrutinizes the act, and sustains it only when there is found to have been capac ity sufficient for the act in question and en tire freedom of will. Consequently such cases usually include the two elements of mental incompetency of some degree and undue influence; and probably a majority of the cases in which the aid of equity is sought to set aside deeds on the ground of undue influence involve also the question of the existence of senile dementia to a greater or less extent. The principle upon which courts of equity deal with this class of per sons is neither as a. matter of course to af firm or avoid their acts, but to protect them in the exercise of such capacity as they have. It will scrutinize their transactions; consid ering the nature of the act done, the induce ments leading to it, and the attending cir cumstances and influences. If the conscience of the court is satisfied that such a grantor comprehended the nature and consequences of the transaction, and exercised a deliberate and free judgment, it will be sustained ; but if the nature of the act or the attending circumstances justify the conclusion that the grantor's weakness has been taken ad vantage of, the deed will be set aside in equity however valid it might be at law; 1 Bro. Ch. 560; 1 Knapp 73; Cruise v. Chris topher's Adm'r, 5 Dana (Ky.) 181; Wilson v. Oldham, 12 B. Monr. (Ky.) 55; Tracy v. Sacket, 1 Ohio St. 54, 59 Am. Dec. 610;
Gass v. Mason, 4 Sneed (Tenn.) 497. "It may be stated as settled law, that whenever there is great weakness of mind in a person executing a conveyance of law, arising from age, sickness, or any other cause, though not amounting to absolute disqualification, and the consideration given for the property is grossly inadequate—a court of equity will . . . interfere and set' the conveyance aside ;" Allore v. Jewell, 94 U. S. 511, 24 L. Ed. 260 ; 1 Sto. Eq. Jur. § 238; Bisph. Eq. 288. For a thorough examination and dis cussion of the subject in a case of senile de mentia in which a deed was set aside, see Jones v. Thompson, 5 Del. Ch. 374. In that case Saulsbury, Ch., thus stated the prin ciple upon which courts of equity deal with such cases : "In cases of alleged mental incapacity, the test is whether the party had the ability to comprehend in a reason able manner the nature of the affair in which he participated. This is the rule in the ab sence of fraud. . . . This- ability so to comprehend necessarily implies the power to understand the character, legal conditions, and effect of the act performed. . . . The cause of mental weakness is immaterial. It may arise from injury to the mind, tem porary illness, or excessive old age. In such cases any unfairness be promptly re dressed." In a very similar case a deed was set aside on the ground of mental incapacity of the grantor by reason of senile dementia or dotage, by Bland, Ch., whose opinion con tains an elaborate discussion of the different species of dementia, which he classifies as, Idiocy, Delirium, Lunacy, and Dotage, un der which latter term he describes senile de mentia.
See INsemry.