is predicated mainly upon statements of facts made to
him by the attending physician, out of the patient's pre-
sence, for the purpose of a professional examination of
the patient. But if the attending physician is himself a
witness, or if the facts are testified to by others, the
opinion of the consulting physician upon the hypothesis
of the existence of such facts in addition to those within
his own observation, is admissible. In a criminal trial,
the opinion of one expert as to whether a certain state of
facts was enough to justify another expert in the forma-
tion of an opinion to which the other had testified, was
held to be inadmissible.2

And, after a witness has been admitted to testify as an
expert, evidence can not be given to the jury of the
opinions of other experts in the same science, as to whether
the witness was qualified to draw correct conclusions in
the science on which he had been examined, though such
testimony might have been properly offered to the court
to show the competency of the witness before he was
admitted to testify. The rule imposing limitations upon
such opinions, is now well established, and the expert's
own character is best protected by it, under the maxim
of experto crede, since, whatever might be said by one
expert in derogation of another's opinion, might in turn.
be said of his own; mutato nomine de te fabula narratur.
As might be inferred from this, experts are never per-
mitted to state their views on matters of legal or moral

Whetherbee's Exrs. v. Wetherbee's Heirs, 38 Verm. 454.

But the interrogatories to such medical persons must be so framed as not to elicit, and their answers so given as not to contain, any expression of opinion by them on the credit of the witnesses or truth of the facts testified to by others. Livingston's case, 14 Gratt. 592.

2 People v. Hartung, 17 Howard Pr. R. 151.

3 Tullis v. Kidd, 12 Alab. 648.

Egati

would artion

me

TH

E OF SKILLED TESTIMONY.

- statements of facts made
ician, out of the patient's
a professional examination
ttending physician is himself
are testified to by others.
physician upon the hypothes
acts in addition to those wi
Imissible. In a criminal tr
as to whether a certain si
Ty another expert in the fi
ch the other had testified, r

s been admitted to testify as
be given to the jury of
the same science, as to whet
to draw correct conclusions
ad been examined, though s
en properly offered to the cor
of the witness before he

e rule imposing limitations p
ll established, and the exper
tected by it, under the mar
whatever might be said by
another's opinion, might in t
to nomine de te fabula narrav
m this, experts are never pe
ws on matters of legal or m

rbee's Heirs, 38 Verm. 454.
medical persons must be so framed as 25
given as not to contain, any expressie
the witnesses or truth of the facts tes

14 Gratt. 592.

d Pr. R. 151.

obligation, nor on the manner in which other persons would probably be influenced, if parties acted in some particular way. And on similar principles the opinions of medical practitioners upon the question whether a certain physician had honorably and faithfully discharged his duty to his brethren have been rejected.1

The reason of these adjudications is founded in the principle that experts have no proper concern with the merits of a controversy, and no right consequently to express any opinions upon a purely ethical proposition. In delivering such extra professional opinions, they clearly transcend the sphere of their medico-legal duties, and usurp the province of both court and jury. It is for these reasons that they are not allowed to sit in judgment upon the moral conduct of others, or to express their views upon matters not directly germane to their duties as skilled witnesses.

§ 118. Dealing exclusively with facts, and not with opinions, it is made the duty of the expert to endeavor to enlighten the court by stating the data upon which his conclusions are founded. There must be some evidence, even though not completely comprehensible to others, why he has arrived at some particular opinion rather than at any other. Because, if any other opinion were possible, the party to whose advantage it might enure has the right to insist that it shall not be withheld. It is, therefore, the entire evidence adduced in support of the controverted issue which forms the essential foundation upon which an expert can alone base his opinion, since this latter is to be weighed in relation to its correspondence with the facts thus elicited, not being in itself conclusive as to them,

1 Campbell v. Rickards, 5 B. & Adolph. 840; Ramadge v. Ryan, 9 Bingh. 333.

10

and in a late case in Vermont where this point was
mooted, the court said that, "The opinion of experts was
evidence to be considered by them in connection with the
other evidence bearing on the subject, but was not of
itself conclusive; that the value of the rule of law, per-
mitting them to testify their opinion, was grounded on
the fact that generally such opinion was correct; that the
value of such opinion was to be determined by the jury,
having reference to the skill and competency which the
witness manifested, in connection with the other evidence
which was before them to be considered in determining
whether the disputed letters were in the plaintiff's hand-
writing; that experts were not infallible; generally their
opinion was reliable, but they sometimes were wrong."

2

"In evidence of opinion," says Mr. Dickson, "it is essential to ascertain precisely the data on which the witnesses proceed. For example, a physician often forms his opinion as to a supposed disease, partly from the symptoms which he observed himself, and partly from statements by the patient as to his sufferings, and statements by another medical attendant or a sick-nurse. He may also have proceeded upon examination of evacuations or blood, which he was informed came from the patient. Nearly all his data will thus have come to him at second hand, and may have been fabricated or erroneous. He ought therefore to be examined with reference to different combinations of these supposed facts, corresponding to the different results at which the jury may arrive regarding their authenticity. In like manner, a written medical report ought to bear on its face the data on which the opinions contained in it proceed. Its proper purpose is to set forth the inference deducible by a medical man

from

be

be

Vermont where this point at, "The opinion of experts by them in connection with on the subject, but was not Le value of the rule of law, their opinion, was grounded ch opinion was correct; that i s to be determined by the j skill and competency which nnection with the other evide Lo be considered in determi tters were in the plaintiff's b ere not infallible; generally th they sometimes were wrong. ion," says Mr. Dickson, "t recisely the data on which example, a physician often fi pposed disease, partly from t served himself, and partly fre nt as to his sufferings, and st al attendant or a sick-nurse. E - upon examination of evacuatis informed came from the patie thus have come to him at secon E en fabricated or erroneous. amined with reference to differ pposed facts, corresponding to th h the jury may arrive regard like manner, a written med n its face the data on which t proceed. Its proper purpose =nce deducible by a medical 2 Dickson's Evid. vol. 2, § 199

183.

from facts observed by himself. But if any information which he has derived from other sources would, if true, modify his opinion, he should state the results at which he would arrive, on the hypothesis of the information being wholly or partially correct."

§ 119. These fundamental principles governing the testimony of skilled witnesses have been frequently affirmed in various ways by American courts. At the outset of any such evidence, and even though unsolicited, an expert may give the grounds and reasons of his opinion. in his examination in chief, as well as the opinion itself.1 And it is in fact so far made his duty to do so by the very nature of the testimony itself, that it has been held that a physician should state the reasons of his opinion and the facts on which it is based, and if not sustained by them, it is entitled to little weight.2 Testes rationem scientiæ reddere teneantur.3 But in order to make the opinions of experts admissible, they must be founded on a given state of facts, which should embrace all the facts relied upon to establish the theory claimed. Wherever these facts are controverted, they can not be properly considered as affording the witness any opportunity of forming a conclusive opinion; for, as in the case of any other syllogism, if the premises are not admitted the conclusion can not be drawn absolutely. Hence experts are not allowed to give their opinions upon the case where 'Keith v. Lothrop, 10 Cush. 453.

2 Clark v. State, 12 Ohio, 483.

Medical testimony, as to the injuries likely to be produced under a given state of facts, is properly admitted, where the witness states the precise facts on which he bases his opinion, and the court does not withdraw from the jury, the right or liberty to consider whether these facts are established by the testimony. Wendell v. Troy, 39 Barb. 329.

3 Heineccius ad Pand. pars. IV. ? 144.

Lake v. People, 1 Parker (N. Y.) 495.