*555 By the Court,
Dean, J. —The prisoner, on the seventh of June, 1853, at LaGrange, in Dutchess county, in the day time, killed his wife, or the woman with whom he cohabited, and their two infant children, these constituting his whole family. He then, with a sword and motions and language, standing at an upper window in his house, almost entirely naked, kept the people who had gathered around for the purpose of arresting him, from accomplishing their object, until he was shot. He was soon after the occurrence indicted for murder, and at the Dutchess Oyer and Terminer, in September last, tried and convicted. The defence, as usual, in cases of open, aggravated crime, was insanity. Whether the prisoner was or was not of sound mind at the time of the commission of the act, is a auestion with which this court has now no concern. The jury passed upon it, and had there been no questions of law arising upon the admission or rejection of evidence on the trial, it is very clear that their verdict could not, and should not, be disturbed by us. But the prisoner’s counsel on the trial offered evidence which was excluded, and the district attorney was allowed to give evidence after objection on the part of the de-fence. To these various decisions of the court, exceptions were taken, and we are now away from the hurry and excitement of the trial, to pass upon these exceptions. If any one of them taken to material testimony is valid, it is our duty to grant a new trial, no matter what may have been the prisoner’s crime, or what opinion we may entertain of his guilt. The safety of any system of jurisprudence depends upon the uniformity of its administration. By the one which it is our duty to administer, the vilest criminal is entitled alike with the purest citizen to the benefit of all the forms of proceeding, which the wisdom of our predecessors has established as safeguards for the protection of property, liberty and life. Without, therefore, in any way expressing an opinion upon the correctness of the verdict of the jury, I proceed to the examination of the questions which have been raised before us on the argument of this case.
There are very many of the exceptions which can not be sustained There are, however, some of them which the court *556are unanimously of opinion are well taker., and on which I shall now give the conclusion to which on examination I hav<= arrived; I shall also speak of two of the exceptions which Í think can not b.e sustained.
Where the question to be determined by a jury is the sanity of a person, both the acts and declarations of the person are evidence, for the purpose of ascertaining the state of mind of the actor. On the trial of this indictment, this rule was observed, and full latitude was given to the acts, conduct and declarations of the prisoner, both before and after the homicide. His counsel, however, proposed to go further, and prove the effect which the prisoner’s conduct had on the mind of another person the day before the killing, not only by the acts, but by the declarations of the person killed, made to third persons, and in the absence of the prisoner. I can find no authority-which would justify this species of evidence, and there is no reason which can sustain it. The fact to be proved is the state of the prisoner’s mind. While his declarations at the time and before and after the occurrence, are evidence, not of the res-gestce, but of the fact to be proved — the mental state of the prisoner — it is very clear that the declarations of third persons can not shed a ray of light on the subject of inquiry, but will, at best, furnish the jury with only the opinion of the declarant. Had the person whose declarations are sought thus to be given, survived, her opinion under oath would not have been testimony. Upon what principle, then, can her statements be given in evidence, without the means, by a cross-examination, or in any other way, of testing their accuracy, or ascertaining the sincerity with which they were uttered? These declarations constitute no part of the res-gestce. They are of a day prior to the transaction, and are claimed to be evidence, not of the fact to be proved — the state of the prisoner’s mind — but of the feelings and emotions of the deceased; a matter which is wholly immaterial to the issue on trial. Suppose what is sought to be proven by this evidence is admitted, that deceased said she was alarmed and feared the, prisoner would hurt himself, does that advance the jury a single step in the® inquiry? Do not. sane *557men frighten women? Or are all men who alarm their wives exempt from criminal liability? The mere statement of the conclusion to which this species of evidence would bring us, is a sufficient argument to show its inadmissibility.
Another ground of error, which is confidently relied on by the prisoner’s counsel, is the admission of a record of conviction for petit larceny more than twenty-five years old, against one of the witnesses on the trial. While I am not aware of any statute of limitations which would exclude this, I am very certain that such testimony, not followed by proof of subsequent bad character, ought to be wholly disregarded by a jury. To give it weight and say that a person who had once been guilty of an offence which in itself does not render a witness incompetent, is for life to be discredited, would be to declare that repentance and reformation were impossible, and at the same time take away one of the strongest motives for reform. I can not believe that any jury could have been influenced by this testimony, to discredit the witness against whom .it was produced.
I think there was error in the rule adopted for the examination of medical witnesses. Several of those who had heard only a portion of the testimony on which the prisoner’s counsel relied to establish his defence were allowed to give their opinions founded upon the part of the testimony they had heard as to his sanity. Although the opinions of experts are admissible evidence, yet it must be on a given state of facts,- and the facts on which the opinion is based must be admitted, and must be all the facts relied upon to establish the theory which it is supposed these facts sustain. Every witness would otherwise come to a different conclusion, and the same witness testifying on one half the facts might give as his opinion that they indicated sanity, while the other half would satisfy him of the prisoner’s madness. A question in physical science will afford an illustration. A motion which is the result of a combination of different forces, invariably changes its direction if but one of the moving powers is withdrawn. Take away half of them, it would be reversed in its course. Experts might be called to *558prove any given motion; they might also be asked what would be the effect of certain combined forces, but in either case it is manifest that to have the opinion correct, all of the motive powers must be given. Medical men are allowed to give their opinions in cases of alleged insanity, because they are supposed by their study and practice to understand the symptoms of insanity and possess peculiar knowledge on this subject, while the jury whose opinion is ultimately to govern in the decision of the question, are believed to be incapable, without the aid of the experience and skill of these men, to judge correctly of mental phenomena. It is for this reason, and for this reason solely, that such testimony is admitted. It is evident, therefore, that if medical witnesses are to tell the jury what is the state of the prisoner’s mind, they must do it on all the testimony which is relied on to establish insanity. And to allow it on a part, would be as dangerous in principle as to permit a juror to sit during a part of the trial and then unite with the rest in determining the verdict. The conclusion to which the members of the court have come on this point is sustained by reason and the authority of every reported case, so far as they have come under my examination or notice.
There is another question of much interest which arose on the trial of this case, on which I think an opinion should be given now. It is this: On a trial where the question of insanity arises, can a medical witness, who is examined as an expert, be asked his opinion upon a hypothetical statement of facts? I -know that such has been the practice on trials of this kind, and am surprised to find no authority on the subject in the reports of this state. By a reference to the trial of Freeman, it will be seen that this mode of examination was adopted without objection. On the trial of this case the prisoner’s counsel propounded to a medical witness, on the cross-examination, seventeen questions, all of which were excluded; some of them were perhaps objectionable in form, but they sufficiently raise the question for us now to settle the principle which should govern, in the admission or rejection of evidence of this nature. I think it is proper to allow the witness to be asked whether a certain state of facts *559if proved or admitted, indicate insanity; and that for the purpose of testing the skill of the witness or the soundness of his knowledge.
On the cross-examination, the counsel may be allowed to ask even whether facts not in proof do or do not indicate insanity. The medical witness will thus not be allowed to pass upon the truth of the facts, nor make up the opinion of the jury, but give his own opinion upon a given state of facts and leave the jury to determine their truth, weigh his opinion and make their own verdict upon the whole. This is equivalent to allowing the professional witness to testify what are the symptoms of insanity, leaving to the jury, as should be done after learning what are the symptoms, to determine the whole question whether those symptoms exist, and if so, whether they are feigned or real, and also their extent.
I think, therefore, that the exceptions above indicated are well taken, and that a new trial should be granted.
Judgment reversed, and new trial granted