Ladd, J.
The plaintiff was on his way to 'Woodstock in a single-seated, one-horse buggy going south, on December 29, 1910. His horse was trotting along when an automobile operated by Robinson approached from the opposite direction, and passed at a distance of between sixteen and twenty feet as estimated by Robinson, or thirty or forty feet as testified by plaintiff: The defendant with his automobile, containing four or five passengers, came up behind plaintiff’s rig, and when Robinson was about opposite, turned his car *334to go between, when the fender struck the back wheel of the buggy, lifting that side up, and caused plaintiff, with the cushion and blanket, to slip or fall out on the ground, and the horse, becoming frightened, went on to Woodstock. The plaintiff testified that he did not stop but had slowed up, and was corroborated by the testimony of Robinson. The defendant testified that plaintiff stopped his vehicle suddenly, as though to converse with Robinson, and his testimony is corroborated by that of the persons riding with him. In this action, recovery is sought on the ground that defendant was negligent (1) in running his car at an excessive rate of speed, (2) in failing to give warning of his approach, and (3) in not keeping far enough from plaintiff’s vehicle to safely pass it without a collision, and that the injury occurred without fault on the part of the plaintiff contributing thereto. The defendant denied having been guilty of any negligence, and alleged that the collision was due to the carelessness of plaintiff in suddenly stopping his horse without any notice or warning to the defendant. The evidence was such as to carry these several issues to the jury. This is apparent from even a casual examination of the record, and for this reason it is not necessary to review the evidence.
1. Evidence : expert testimony : personal injury : cause of pain. I. The plaintiff was attended by Dr. McCauliff. He testified that upon examination made January 3, 1911, he discovered a contusion on the left side of plaintiff’s head, immediately above the temple, with swelling one and one-half or two inches in diameter, somewhat discolored and sensitive to the touch, and also a darkening or contusion of the left lip without much swelling, and that the patient said he sufferred from a severe headache and was troubled with insomnia; that he called on him eight or nine times during that month, and that the headaches became more severe in a few days after his first call and the insomnia more difficult to overcome; that he was of opinion that the witness suffered severe pain from his injuries, and that after the time men*335tioned lie was consulted by the plaintiff about once a week for another month; that he complained of pains in his head during the entire time and of impairment in his hearing and sight. He was then asked “whether or not a violent blow upon the head or concussion from falling, such as would produce this swelling that you speak of on the head, might or might not have any effect upon the hearing, or the head itself, of a permanent nature.” “A. It might.” “Q. To what did you ascribe professionally the continuance of these headaches described that Mr. Strever complains of?” An objection as incompetent, immaterial, and irrelevant was sustained. “Q. Considering the history of the ease as detailed to and what you observed of those injuries in January, what would you say was the cause of these headaches?” A like objection was sustained. “Q. State whether or not a violent blow on the head in the place where you saw his injury would cause continual headaches such as Mr. Strever had or not.” An objection as leading and suggestive, incompetent, and immaterial was sustained. “Q. I wish you would now state from your knowledge of the history of the case and physical condition of Strever as a physician, whether these pains that you have described or the headaches were or were not the result of injury upon his head, that you have referred to in your testimony.” Same objection was sustained. “Q. I now refer to all of this.” A like objection was sustained, and the court remarked: ‘ ‘ This is a question for the jury; they must draw that conclusion, or they must fail to draw it.” Exceptions were saved to each of the above rulings, and all were erroneous. They Called for opinions which it was competent for an expert, if possessed of sufficient information, to answer. The witness had fully qualified, and the rule is well estab- ' lished that though a physician may not testify what the cause of an injury actually was, his testimony as to what might have, within reasonable probability, caused it is received. Thus as to whether an injury might have resulted from an alleged concussion by being thrown from a carriage, Quinn *336v. O’Keeffe, 9 App. Div. 68 (41 N. Y. Supp. 116), or from a blow, 12 Am. & Eng. Ency. Law (2d Ed.) 447. In Barker v. Ry., 51 W. Va. 423 (41 S. E. 148, 90 Am. St. Rep. 808), testimony of a physician that the plaintiff’s condition might have been caused by shock, a fall, or anything that produces a shock to the spinal column was held admissible. See, also, Bennett v. Fail, 26 Ala. 605; Thompson v. Bertrand, 23 Ark. 730; Mo. P. Co. v. Lovelace, 57 Kan. 195 (45 Pac. 590); Oliver v. Ry., 65 S. C. 1 (43 S. E. 307); Matteson v. Ry., 62 Barb. (N. Y.) 364. The subject was one not familiar to the jury, and it was competent to call for expert opinion to aid in tracing the casual connection between plaintiff’s ailments and the efficient cause; and, as a nervous temperament and a fall from a load of tile nearly four months previous v>7ere suggested in cross-examination as such cause, the testimony of the physician who attended him during his illness as to what might have occasioned his suffering was material, and should not have been excluded. The inquiries were not vulnerable to the objection as leading, nor did they call for an opinion as to the ultimate issue to be determined by the jury. AVhether he was in fact injured by the fall from the buggy would necessarily be included in the verdict of the jury, but was not determinative of the case.
2. Highways: travelers: duty to turn out or look behind: negligence. II. In an instruction otherwise unexceptionable, the court told the jury that if an ordinarily careful and prudent man, situated as plaintiff was and in like circumstances, would “have looked and listened or given warning inleWion to stop in the highway, or wou^ have driven out of the beaten track before stopping, and you further find that the plaintiff did suddenly stop in the highway, but did not look, listen, or give warning to the defendant of his intention to stop, and the collision of which he now complains was thereby occasioned, then the plaintiff was guilty of contributory 'negligence, and he cannot recover.” The converse also was stated. The plaintiff testified that he drove out to the *337side of the road, and that he did not stop but merely slowed up. For this reason the instruction might be improved by mentioning these matters hypothetically. Nor are we content with the suggestion of an obligation on the part of a traveler that he must, Janus-like, keep an outlook in the rear or have driven from the portion of the highway along which his vehicle was moving. He was under no obligation to yield any portion of the highway to allow defendant to pass. Elenz v. Conrad, 123 Iowa, 522. Only to avoid a collision reasonably to be apprehended is the foremost traveler bound to turn to one side. His duty is to keep' a lookout ahead, and only when he is aware of a vehicle coming up from the rear, and near that which he is driving, is he charged with duty of exercising ordinary care in the management of his own so as not to injure that behind. Delfs v. Dunshee, 143 Iowa, 381.
If there be not sufficient room it is said to be 'the duty of the foremost traveler to afford it, on request made, by yielding an equal share' of the road, if that be adequate and practicable; if not, the object must be deferred till the parties arrive at ground more favorable to its accomplishment.’ But it is perhaps doubtful whether such duty can be deemed an absolute legal duty, and even if it should be so considered, the failure of the leading traveler to permit it by turning out to one side will not justify the other in purposely running into him or attempting to pass at all hazards. The only rule of general application that can be laid down-is that he who attempts to pass another going in the same direction must do so in such manner as may be most convenient under the circumstances of the ease, and if negligent, and damage results to the person passed, the former must answer for it, unless the latter by his own recklessness brought the disaster upon himself. (2 Elliott on Roads & Streets, section 1084.)
The party coming up from behind must exercise reasonable care to beep his vehicle under control, and far enough in the rear to avoid the contingencies of decreasing speed, stopping and the like. He is in a situation to do this, and' the law casts that burden upon him. Whether plaintiff knew *338defendant was immediately behind his buggy with his automobile, and so close that if he stopped it would likely ruu into his vehicle, was an issue to be submitted to the jury, and if such was the situation and plaintiff was aware of it, undoubtedly he took the risk in suddenly stopping, if he so did, and cannot recover; but if he was not aware that defendant was in such proximity, or if he merely slowed down the speed at which he was driving, then he was not negligent, regardless of whether he looked back or listened. Though the reference to looking and listening, guarded as it is in the instruction, may not constitute reversible error, it may as well be avoided on another trial.
3. Special in terrogatories : failure to answer. III. The jury failed to answer one of the special interrogatories submitted, and error is predicated on the court receiving the verdict without exacting an answer. As plaintiff does not appear to have insisted on an answer being required, he cannot be heard to complain. Huss v. Ry., 113 Iowa, 343; Mayo v. Halley, 124 Iowa, 675; Andrews v. Ry., 77 Iowa, 669.
4. New trial: inadequacy of verdict. IV. The jury returned a verdict of $1, and the plaintiff asked that this be set aside as inadequate. If there were proof of substantial damages, uncontroverted, the motion for new trial should have been sustained. Tathwell v. Cedar Rapids, 122 Iowa, 51; Ward v. Light Co., 132 Iowa, 581. That plaintiff was injured was uncontradieted. He was precipitated from his buggy to the ground, and taken immediately to Dr. Smith’s office and examined. He found no bones broken, and did not remember of any contusion of the skin, but testified that he “was in a dazed condition. The man undoubtedly had had a fall, but I did not discover any lesions.” Upon calling on him a week or two later, the witness said: “All that was wrong was an intense headache and considerable nervousness. I do not know what caused those conditions. . . . The nervousness that I discovered on my call to his *339place might have been due to a number of different causes. I thought he was suffering from grippe and the shock or contusion of this accident. ’ ’ The witness then explained that there might be concussion without external evidence of it; that the time of the examination in his office he complained of his chest, head, and back, that he ! ‘ attributed part of his grief to the accident, but he could have had very much the same condition without any accident at all. It was impossible. to tell the real cause of the headache and nervousness” — and explained that he had complained of sleeplessness a year or two before. The testimony of Dr. MeCauliff -concerning his condition has been stated. He testified further that he attributed his nervousness and sleeplessness to the injuries he found when called to treat him. That plaintiff was confined to his house a part of the time, requiring the care of a nurse for several weeks, was testified by plaintiff, his wife, a son and daughter, and an employee. Indeed there is no controversy on this point, though two physicians, Carver and Sams, examined him at the instance of defendant October 25, 1911, and discovered no trouble with him save a catarrhal condition of the middle ear. He had fallen from a load of tile in September previous, but his testimony that he had recovered therefrom was not disputed. For medicine and medical attendance as a result of this injury he had paid $106.75. There is no room m this record for saying that he did not suffer substantial injuries in falling from the buggy, and that this expense was occasioned thereby, and for this reason, if entitled to anything, he should have been allowed substantial damages. On this ground the motion for new trial should have been sustained. —Reversed.