7. Begin, “This is the last will of me, W. B. of S.”; and end, “and I revoke all former wills and codicils.” Dated this ___________ day of ______________ one thousand, &c. CHAPTER XVI MENTAL UNSOUNDNESS In the whole range of medical jurisprudence there is no subject more interesting, more difficult, or more important than the diagnosis of insanity, and its relation to the criminal responsibility of individuals. It is impossible, in the short space at our disposal, to do more than to offer a few remarks which may assist the student in the elucidation of some of the most important cases which may engage his attention. =Legal Definitions.=--Three forms of mental disorder are recognised in law: 1. _A nativitate, vel dementia naturalis_--idiocy or imbecility. 2. _Dementia accidentalis, vel adventitia_--acquired general insanity, either temporary or permanent, lunacy. 3. _Dementia affectata_, acquired madness from intoxication, &c. (See “Delirium Tremens,” p. 205.) Under the term lunacy are included the mania, monomania, and dementia of medical writers. Another term frequently used in legal proceedings, the meaning of which it is not easy to give, is “_non compos mentis_,” _unsoundness of mind_. According to the late Forbes Winslow, “unsoundness of mind is not lunacy” in the legal acceptance of the phrase. This term was first used in a Statute passed in the reign of Henry VIII., relating to the punishment of treasonable offences, and is defined by the early law text-books to be strictly one who _gaudet lucidis intervallis_--a definition not psychologically exact. The phrase “unsoundness of mind” was first used by the late Lord Eldon to designate a state of mind not exactly idiotic, and not lunatic with delusions, but a condition of intellect occupying a place between the two extremes, and unfitting the person for the government of himself and the management of his affairs. The above definition has been acted upon by other judges--Lyndhurst, Brougham, &c. As a rule, a medical witness will consult his own interest in not attempting to define insanity, bearing in mind the philosophic caution of Polonius, who, when addressing Hamlet‘s mother, says--