Definition: med. jur. That space of time between two fits of insanity, during which a person non compos mentis is completely restored to the perfect enjoyment of reason upon every subject upon which the mind was previously cognizant. Shelf. on Lun. 70; Male s Elem. of Forensic Medicine, 227; and see Dr. Haslam on Madness, 46; Reid s Essays on Hypochondriasis, 317 Willis on Mental Derangement, 151.
2. To ascertain whether a partial restoration to sanity is a lucid interval, we must consider the nature of the interval and its duration. 1st. Of its nature.: "It must not," says D Aguesseau, "be a superficial tranquillity, a shadow of repose, but on the contrary, a profound tranquillity, a real repose; it must not be a mere ray of reason, which only makes its absence more apparent when it is gone, not a flash of lightning, which pierces through the darkness only to render it more gloomy and dismal, not a glimmering which unites night to the day; but a perfect light, a lively and continued lustre, a full and entire day, interposed between two separate nights of the fury which precedes and follows it; and to use another image, it is not a deceitful and faithless stillness, which follows or forebodes a storm, but a sure and steady tranquillity for a time, a real calm, a perfect serenity; without looking for so many metaphors to represent an idea, it must not be a mere diminution, a remission of the complaint, but a kind of temporary cure, an intermission so clearly marked, as in every respect to resemble the restoration of health." 2d, Of its duration. "As it is impossible," he continues, "to judge in a moment of the qualities of an interval, it is requisite that there should be a sufficient length of time for giving a perfect assurance of the temporary reestablishment of reason, which it is not possible to define in general, and which depends upon the different kinds of fury, but it is certain there must be a time, and a considerable time." 2 Evan s Poth. on Oblig. 668, 669.
3. It is the duty of the party who contends for a lucid interval to prove it; for a person once insane is presumed so, until it is shown that he has a lucid interval or has recovered. Swinb. 77; Co. Litt. by Butler, n. 185; 3 Bro. C. C. 443; 1 Rep. Con. Ct. 225; 1 Pet. R. 163; 1 Litt. R. 102. Except perhaps the alleged insanity was very long ago, or for a very short con- tinuance. And the wisdom of a testament, when it is proved that the party framed it without assistance, is a strong presumption of the sanity of a testator. 1 Phill. R. 90;1 Hen. & Munf. 476.
4. Medical men have doubted of the existence of a lucid interval, in which the mind was completely restored to its sane state. It is only an abatement of the symptoms, they say, and not a removal of the cause of the disease; a degree of irritability of the brain remains behind which renders the patient unable to withstand any unusual emotion, any sudden provocation, or any unexpected pressing emergency. Dr. Combe, Observations on Mental Derangement, 241; Halsam, Med. Jur. of Insanity, 224; Fodere, De Medecine Legale, tom, 1 , p. 205, 140; Georget, Des Maladies Mentales, 46; 2 Phillim. R. 90; 2 Hagg. Eccl. R. 433; 1 Phillim. Eccl. R. 84.
See further, Godolph. 25; 3 Bro. C. C. 443; 11 Ves. 11; Com. Dig. Testi-moigne, A 1; 1 Phil. Ev. 8; 2 Hale, 278; 10 Harg. State Tr. 478; Erskine s Speeches, vol. 5, p. l; 1 Fodere, Med. Leg. 205.
Legal Dictionary 
