Day, J.
1. evidence: testimony of experts: hypothetical question. I. The plaintiff describes the accident and injury as follows: “I lit lengthwise of the track, and on my side and back. I tried to step, and the car caught me before I struck the ground. My foot was caught in the cogs, my'leg was broken, and the car passed over me, and I was turned end over end under the car.” In another portion of his testimony the plaintiff speaks of the accident and injury as follows: “In falling, my right foot was caught in the gearing, and my other leg was broken; part of the bone was mashed; both bones were broken; there was an open wound; was hurt on head, gash in side, back and top, and one on eye and on shoulder; breast was hurt in doubling under the car. The foot that was hurt gives out, gets stiff in- walking; there is a large lump on the leader which gets sore in walking. The furthest I have been able to *78walk is between two and three miles, and this takes an hour and a half. My other leg gets weak in walking; think one leg is shorter than the other; the bones seem to have a rough place which I can feel; the ankle of the leg that was broken is weak — it rocks about for want of, support; in stepping on anything slippery I have to give way to avoid hurting; the bone pains me; my breast - is weak, and carrying any weight or stooping over pains me.” This is the fullest account of the injury contained in the evidence. There is no testimony describing it as of a more serious character. The evidence shows that after the accident plaintiff wqs carried on the. hand ear to Newton, and was then placed on a freight wagon with a platform on it, and hauled up town to Bennett’s house. Evidence was introduced tending to show that plaintiff, after he arrived at Bennett’s, admitted that the accident resulted from his own carelessness.
As bearing upon the state of the plaintiff’s mind at the time, of making this admission, the plaintiff introduced Dr. Way, a graduate of a medical school, who had been a practicing, physician about six months, and asked the following question: “Sujjpose a young man of good, healthy physical condition should fall down, or in riding along on a hand car should fall down in front of it, and one of his feet being taken up or caught, between the cog wheels and the platform, and ground rq> about half-way, just gradually eaten off, so as to leave the large toe on and take the rest of it off, the other leg being broken, crushed, both bones of the tibia, and that in that condition,, lying with his head forward on the track, lengthwise, his feet being taken up or caught in the oar with five men on it, and his, extremities being brought up so that he was doubled over in this way under the car (indicating), his head lacerated, having wounds on the scalp, his shoulders bruised; suppose that then that young man was taken up and placed on a hand car, and, in August, taken a distance of about two miles, and, about two hours after that time — that is, an hour after the' occurrence — laid upon a lumber wagon, with nothing on it but *79a common board platform, and taken from thence about three-quarters of a mile, and then taken off by the crowd, what would you say, doctor, to that young man’s mental condition, and his capacity for intelligently comprehending and understanding what he was talking or saying with reference to this occurrence on the hand car, and how he received the injury ?” This question was objected to upon the ground that the evidence does not disclose the state of facts given in the hypothetical question. The objection was overruled, and defendant excepted. The witness answered: “I don’t suppose, from general principles, that he would be in a rational condition. ” This question should have been excluded. It presents for the opinion of the witness circumstances of which there is no evidence whatever. It contains a greatly exaggerated statement of the injury and its attendant circumstances. It is not competent to state to a witness any hypothetical state of facts of which there is no proof, and ask his opinion based upon such facts. Such proof would clearly be irrelevant and incompetent. A physician may give his opinion as to the sane or insane condition of a person’s mind, and such opinion is admissible, though the witness founds it, not on his own personal observation, but on the case itself, as proved by other witnesses on the trial. But an expert cannot be allowed to give his opinion upon a case based upon statements made to him by parties out of court and not under oath. 1 Green-Leaf on Evidence, § 440, and note. If an expert cannot base an opinion upon statements made to him out of court, by parties not under oath, we know of no principle upon which he should be permitted to base an opinion upon a statement made to him by an attorney in court, in the trial of a cause, which is altogether without support in the evidence.
In Muldowney v. The Illinois Central Railway Company, 39 Iowa, 615, it is said: “A medical man’s opinion is very competent when the facts upon which it is based are testified to by himself or others, but his opinion without the facts is not competent, because he is not authorized to find or assume the facts *80at his pleasure. ' They are to be found by the jury, and if they do not exist as he assumes, then his opinion may go for naught. ” If the expert may not find or assume the facts at pleasure, it must be equally improper for the attorney of a party to do so. We do not mean to say that the facts upon which the opinion of an expert is sought must be proved. It is sufficient if there be evidence tending to establish the facts. Then the jury must determine whether or not the evidence submitted proves the facts upon which the opinion is based. What we determine is, that an opinion cannot be based upon a fact of which there is no evidence.
II. Defendant read in evidence so much of the affidavit for continuance as states that Jerome Allen would swear that he saw plaintiff when he came in on the hand car, and helped remove him to the wagon, and was with him in the wagon, and that during that time he repeatedly said no one was to blame for the accident but himself, and that if he had not been trying to show off he would not have been hurt. The defendant further offered to read from said affidavit that the witness would swear that said Hurst was at that time rational and of sound mind, and made the statements fully understanding what he was saying. The plaintiff objected to this offered testimony as incompetent. The objection was sustained. The defendant excepted. It does not appear that Allen was qualified to testify as an expert. Under the doctrine of State v. Geddis, 42 Iowa, 264, and State v. Stickley, 41 Iowa, 232, we think it was not competent for Allen to state his opinion as to Hurst’s mental condition.
2.___: leading question. III. The defendant introduced as a witness John Burnett, who testified as to certain admissions made by the plaintiff after the injury respecting the accident. The witneg3 wag then asked the following question: “You may state what he said, if anything, about trying to show off before the bridge hands?” This question was objected to as leading and suggestive. The objection was sustained. The defendant excepted and assigns the ruling as error. A lead*81ing question is one which suggests the answer desired. “In New Hampshire it is said that a question, to be leading, must instruct the witness how to answer, or put words into his mouth to be echoed bach, or in some way suggest the answer desired, and that a question calling for a direct affirmative or negative is not leading, unless it suggest one more than the other. ” 1 Greenleaf on Evidence, §§ 434 and 434 a. Spear v. Richardson, 37 N. H., 23; Page v. Parker, 40 N. H., 47. The question under consideration is not, we think, vulnerable to the objection urged. If it is competent only to ask a witness what was said at a particular time, without directing the witness to the subject deemed material, it is evident that examinations would be very greatly protracted, and cases would be greatly incumbered with irrelevant and immaterial testimony. The rule inhibiting the asking of leading questions must be understood in a reasonable sense, and must have a reasonable construction.
Several other questions arising upon the introduction of the testimony are presented, -which we do not deem it necessary to consider separately. We may say, however, that in a number of other, not, perhaps, very important matters, the defendant, both in the introduction of testimony in chief and in the eross-examipation of the witnesses of the plaintiff, was confined within too narrow limits.
3. railroads: negligence: change of service. IV. Evidence was introduced tending to show that iat the time the injury was sustained the plaintiff and the other employes in charge of the hand car had completed their day’s work for the defendant, and that they were off of the section on which they had been employed, and were going to Newton with the hand car for provisions for the section boss. Respecting this branch of the case the court instructed the jury as follows :
“22. Where the employes of a railroad company voluntarily go off of their section on business of their own, disconnected from the business of the company, while such employes are so engaged the company is not liable for any -accident *82or injury which, may occur to them, from whatever cause the same may arise.
“23. But where an employe of a railroad company working on a section under a foreman or boss is, by such foreman, required to go off of the section on which he contracted to work, and perform duties apparently in the line of his employment, the same liability attaches to the company for injuries received by such employe while off his proper section as while on it.”
As applied to the evidence in this case we think this last instruction was calculated to mislead the jury. The doctrine is elementary, that a principal is bound by the acts of his agent only when they are within the scope of the agent’s employment, or the conduct of the principal respecting the agent has been such as to furnish third persons reasonable ground for believing that the agent was acting within the scope of his employment. If the boss in charge of this section had simply taken the plaintiff off of his section to work for the defendant on another part of its road, we think the defendant might well be held liable for injuries.sustained on such portion of the road through defendant’s negligence. But if the plaintiff was taken off of the section to perform a service for the boss individually, we think the defendant cannot be held liable unless its course of conduct was such as to furnish a reasonable ■ ground for believing that the section boss had authority from the company to engage the plaintiff in such employment. If this is what was meant by the court in the use of the language employed in the instruction, the principle involved in the instruction is not erroneous; but, as the case must be reversed for the other reasons assigned, we think this instruction should, upon the retrial, be so modified as to express the idea above conveyed.
Reversed.