Under the plea of not guilty, evidence was introduced by him for the purpose of showing: First, that at the time of the killing he was incapable, by reason of unsoundness of mind, of committing any criminal offense; second, that at most the killing was "Upon a sudden quarrel or heat of passion," and therefore he could not be found guilty of any higher offense than voluntary manslaughter; third, that at the time of the killing he had reasonable ground to apprehend, and did apprehend, that the deceased was about to do him great bodily harm