(1)  A person is not criminally responsible for an act done or an omission made by him –

(a) when afflicted with mental disease to such an extent as to render him incapable of –

(i) understanding the physical character of such act or omission; or

(ii) knowing that such act or omission was one which he ought not to do or make; or

(b) when such act or omission was done or made under an impulse which, by reason of mental disease, he was in substance deprived of any power to resist.

(2)  The fact that a person was, at the time at which he is alleged to have done an act or made an omission, incapable of controlling his conduct generally, is relevant to the question whether he did such act or made such omission under an impulse which by reason of mental disease he was in substance deprived of any power to resist.

(3)  A person whose mind at the time of his doing an act or making an omission is affected by a delusion on some specific matter, but who is not otherwise exempted from criminal responsibility under the foregoing provisions of this section, is criminally responsible for the act or omission to the same extent as if the fact which he was induced by such delusion to believe to exist really existed.

(4)  For the purpose of this section the term mental disease includes natural imbecility.