Plaintiffs’ assignments of error relate solely to exceptions taken to several portions of the trial court’s instructions to the jury. As the doctrine of res ipsa loquitur is applicable to the facts of the case and critical to an understanding of the alleged errors in the jury charge, we will first review the law in this area.
. , A surgeon is not ordinarily an insurer of the success of his operation, and in malpractice actions there is generally no presumption of negligence in the failure to successfully effect a remedy. Starnes v. Taylor, 272 N.C. 386, 158 S.E. 2d 339 (1968); Pendergraft v. Royster, 203 N.C. 384, 166 S.E. 285 (1932). There is, however, an exception to this rule. When the facts of the case manifest such obvious lack of skill and care, they may afford in themselves an inference of negligence, thereby invoking the doctrine of res ipsa loquitur. The doctrine of res ipsa loquitur has been recognized to apply in actions for malpractice where a surgeon has left a foreign object or substance in a patient’s body after an operation. Mitchell v. Saunders, 219 N.C. 178, 13 S.E. 2d 242 (1941); Pendergraft, supra. A surgeon is under a duty to remove all harmful and unnecessary foreign objects at the completion of the operation. Thus the presence of a foreign object raises an inference of lack of due care. If the facts of the case justify the application of the doctrine of res ipsa, the nature of the occurrence and the inference to be drawn supply the requisite degree of proof to carry the case to the jury without direct proof of negligence. Young v. Anchor Co., 239 N.C. 288, 79 S.E. 2d 785 (1954). The effect of the doctrine of res ipsa, while not relieving *290the plaintiff of the burden of proof, is significant. It enables the plaintiff to make out a prima facie case by furnishing some evidence, an inference, of want of care. Mitchell, supra.
[1] Turning now to the present case, the threshold question is whether plaintiffs offered sufficient evidence at trial to invoke the doctrine of res ipsa loquitur. We have examined the record carefully, focusing our attention primarily on defendant’s contention that an 8-V2 inch wire was present in Mrs. Hyder’s body prior to the cutdown procedure performed on 6 October 1975. There is some merit to defendant’s position inasmuch as Mrs. Hyder underwent a similar cutdown procedure on 6 August 1975. However, numerous X rays were taken of Mrs. Hyder’s chest and abdominal area between 6 August and 6 October. Based on these X rays there is ample credible testimony from the physician who performed the first procedure, as well as from the hospital radiologist, that no foreign object, specifically an 8-V2 inch wire, was then present in Mrs. Hyder’s body. Between 6 October and 17 November no X rays were taken. The 17 November X rays and those taken subsequently show the radiopaque marker of the wire first within the upper chest area, then later in the abdominal area, and finally embedded in the liver. We are satisfied that defendant’s evidence does not rebut these findings.
Where the plaintiffs have established, by credible proof, circumstances from which a reasonable mind might infer that the wire entered as a result of the 6 October cutdown, they are entitled to a res ipsa instruction unless defendant offers some explanation which as a matter of law destroys the probative force of these circumstances. A defendant’s evidence in explanation has been held not to rebut the presumption arising under the doctrine of res ipsa, but merely to raise an issue for the determination of the jury. Moreover, where a defendant’s negligence appears to be the more probable explanation of the injury, the plaintiff need not exclude all other persons who might possibly be responsible. See Mitchell, supra. See also Mondot v. Vallejo General Hospital, 152 Cal. App. 2d 588, 313 P.2d 78 (1957); Johnson v. Ely, 30 Tenn. App. 294, 205 S.W. 2d 759 (1947). We conclude that the presence of an 8-V2 inch stainless steel wire embedded in Mrs. Hyder’s liver, allegedly there as the result of a cutdown procedure performed by defendant, is so inconsistent with the exercise of due *291care as to raise an inference of lack of care. Plaintiffs were therefore entitled to an instruction on the law of res ipsa loquitur.
[2] In his charge to the jury, the trial judge instructed in part on the doctrine of res ipsa as follows:
[I]f an object such as a wire causes an injury and is shown to be under the exclusive control of the defendant and the incident is such as in the ordinary course of things does not happen if the party having it under his control uses the proper care, (the principle of res ipsa loquitor [sic], which means the thing speaks for itself, in such a case carries the question of negligence to the jury). [Parentheses ours.]
Plaintiffs take exception to this instruction in that it fails to include the following statement, which would appear before the material enclosed in parentheses: it furnishes or would he some evidence, in the absence of explanation of the defendant, that the accident arose from want of care. Lea v. Light Co., 246 N.C. 287, 98 S.E. 2d 9 (1957); Pendergraft, supra. We agree that the trial judge erred in the omission of this statement.
The trial court’s incomplete instruction deprived plaintiffs of the full advantage of the law upon which they rightfully relied. An instruction on res ipsa must include sufficient information to apprise the jury of the theory and significance of the doctrine. Of particular significance is the fact that the burden is on the defendant to come forward with an explanation of the events giving rise to the inference of lack of care. Absent an explanation satisfactory to the jury, it is incumbent upon them to consider defendant’s acts as some evidence of lack of care. Mitchell, supra. We hold that plaintiffs were prejudiced by the trial judge’s error in omitting from his instructions a reference to defendant’s burden of explanation and the inference to be drawn therefrom.
[3] Plaintiffs next take exception to the trial court’s instruction that the only way the jury could properly find the standard of care for a physician on the facts of the case was “through evidence presented by practitioners who were called as expert witnesses.” Plaintiffs contend that expert testimony is not necessary to establish the standard of care on these facts. We agree.
*292“Although no inference of the doctor’s negligence usually arises upon proof of injury or other adverse consequence from treatment or medication, some results are so far out of the ordinary as to permit the jury, without the aid of experts, to find negligence.” Byrd, Proof of Negligence in North Carolina, 48 N.C.L. Rev. 452, 465 (1970). Expert testimony is not necessary when the result is so inconsistent with care or when “the judgment of the reasonableness of what the doctor has done is clearly within the competence of the layman . . ..” Id. See also Pendergraft, supra.
The facts of this case gave rise to the inference that the defendant doctor did not exercise due care. By imposing an external standard established by expert testimony, the trial court essentially negated this inference to plaintiffs’ prejudice.
[4] Plaintiffs also except to that portion of the trial judge’s final mandate which appeared as follows:
Even if you find that a wire segment was found in the plaintiffs body several months after the cutdown procedure, but plaintiff has failed to satisfy you by the greater weight of the evidence that defendant failed to exert his best judgment, skill and ability, it would be your duty to answer the first issue [negligence] No. [Emphasis supplied.]
The defect in this instruction is that it directed the jury to find against the plaintiffs if they failed to prove only one of the three requirements defendant was obligated to comply with in rendering professional services to Mrs. Hyder.
A physician or surgeon who undertakes to render professional services must meet these requirements: (1) He must possess the degree of professional learning, skill and ability which others similarly situated ordinarily possess; (2) he must exercise reasonable care and diligence in the application of his knowledge and skill to the patient’s case; and (3) he must use his best judgment in the treatment and care of his patient. If the physician or surgeon lives up to the foregoing requirements he is not civilly liable for the consequences. If he fails in any one particular, and such failure is the proximate cause of injury and damage, he is liable.
*293 Hunt v. Bradshaw, 242 N.C. 517, 521-22, 88 S.E. 2d 762, 765 (1955) (citations omitted). The trial court only instructed on the third requirement. Plaintiffs would be entitled to recover if they proved defendant failed to comply with any one of the three requirements. Plaintiffs. were entitled to such instruction in the final mandate, and the court’s failure to so charge is prejudicial error.
Defendant points out that the language used in the trial judge’s final mandate (quoted above) parallels that approved of in Pendergraft. In Pendergraft, however, the defendant appealed, alleging as error the trial court’s charge to the jury upon the doctrine of res ipsa loquitur. In commenting on that portion of the charge to which we now refer, the Court found it “as favorable to defendant as could be asked for under the authorities.” 203 N.C. at 397, 166 S.E. at 291. There is nothing in the case to suggest that had the plaintiff taken exception, the Court would have similarly approved the language.
This case involved a highly complex and lengthy trial in which plaintiffs were entitled to rely upon the doctrine of res ipsa loquitur. We note that after an hour of deliberation the jury returned for clarification of the definition of negligence. At this time the trial judge repeated the erroneous instructions. Under these circumstances we must find that plaintiffs are entitled to a new trial.
New trial.
Judges MARTIN (Robert M.) and BECTON concur.