John J. Oilman appeals from a judgment dismissing his medical malpractice action *654against Dr. Frank E. Berridge, a surgeon. A jury determined that Dr. Berridge was not negligent in his care and treatment of Oilman. Oilman contends that the trial court erred in the following respects: (1) refusing the requested instruction on res ipsa loquitur; (2) refusing the falsus in uno instruction; (3) excluding opinion testimony of nurse Kathleen M. Roos; (4) striking opinion testimony or Dr. Fetherston; and (5) denying Oilman's motion to compel discovery of a letter in Dr. Berridge's possession containing Board of Inquiry conclusions concerning his surgeries. We affirm on all issues.
BACKGROUND
Oilman adduced evidence at trial that on August 14,1983, Dr. Michael P. Fetherston, Oilman's treating physician, admitted Oilman to the hospital for an intestinal obstruction. Because Dr. Berridge had performed various intestinal surgeries on Oilman in the past, Dr. Fetherston notified Dr. Berridge of Oilman's hospitalization. On August 23,1983, Dr. Berridge performed surgery on Oilman. During that operation, Dr. Berridge encountered numerous adhesions in Oilman's abdomen that were the result of radiation treatments for a previous cancerous condition. In his attempt to free the adhesions, Dr. Berridge nicked Oilman's small intestine at least twice, spilling fecal matter into the abdominal cavity. Dr. Berridge also nicked Oilman's gallbladder, necessitating its removal. As a result of the complications of the first surgery, Oilman developed an abscess in his abdomen, necessitating emergency surgery on August 31, 1983. During that second surgery, Dr. Berridge made an incision, entered it by hand, and inadvertently damaged Oilman's spleen, necessitating its removal. Dr. Berridge then re*655opened the incision from the first operation, and drained an abscess.
As a result of the first operation, Oilman was left with a one-quarter inch stoma, an abdominal opening for fecal discharge, which is not long enough to allow a proper seal between the stoma and the ileostomy pouch that Oilman wears.1 Thus, Oilman experiences unpredictable fecal leaks that have affected his lifestyle. Oilman argued that Dr. Berridge was negligent in his failure to install a drain tube in the gallbladder site, in his premature order to discontinue antibiotics, and in his failure to examine Oilman after the first surgery to locate the source of Oilman's abdominal pain.
RES IPSA LOQUITUR
Oilman argues that the trial court erred when it rejected his request for submission of a res ipsa loqui-tur instruction to the jury. At the jury instruction conference, Oilman argued that the instruction was necessary because his expert could not testify to any particular act of negligence in the second surgery.2
*656The res ipsa loquitur instruction should be given when:
(a) either a layman is able to determine as a matter of common knowledge or an expert testifies that the result which has occurred does not ordinarily occur in the absence of negligence, (b) the agent or instrumentality causing the harm was within the exclusive control of the defendant, and (c) the evidence offered is sufficient to remove the causation question from the realm of conjecture, but not so substantial that it provides a full and complete explanation of the event.
Lecander v. Billmeyer, 171 Wis. 2d 593, 601-02, 492 N.W.2d 167, 170-71 (Ct. App. 1992). While the "[g]iving of the res ipsa loquitur instruction in general is a question of law which this court reviews independently," we give deference to the trial court's discretionary determination that the evidence offers a full and complete explanation of the event. Id. at 602, 492 N.W.2d at 171. In this case, the trial court reasoned that the instruction was inappropriate because Oilman had introduced specific acts of alleged negligence which fully explained his injuries and the evidence left no inference to be drawn by the jury. We affirm the trial court's discretionary determination.
Dr. Sheldon Morris Solochek, Oilman's expert, testified that the injuries suffered by Oilman as a result of the second surgery were the unnecessary incision and the unnecessary removal of the spleen. Dr. Solochek testified that the extra incision could have been avoided if Dr. Berridge had conducted an examination *657of Oilman's abdomen before surgery to locate the source of Oilman's pain. Dr. Berridge's failure to examine Oilman, in Dr. Solochek's opinion, was a deviation from the standard of ordinary care.
Dr. Solochek attributed the removal of the spleen to the manner in which Dr. Berridge approached the spleen after making the incision. Dr. Solochek testified:
Well, there again the way the spleen was approached, he blindly — knowing that once you— The spleen is such a fragile organ that if you're going to put your hand above it and tear up adhe-sions, you're going to rupture the capsule almost a hundred percent, and you're going to get massive bleeding, and so doing it the way apparently it was done by the operative report, I find that to be a departure from the standard of care also.
The "blind" approach to the spleen, like the "blind nasal intubation" in Lecander, 171 Wis. 2d at 604, 492 N.W.2d at 171-72, was the alleged specific act of negligence that caused the unnecessary removal of the spleen.
From the evidence, we are satisfied that the trial court acted within the ambit of its discretion when it determined that the evidence provided a full and complete explanation of the injuries suffered by Oilman during the second surgery. Thus, we affirm the trial court's refusal to give the res ipsa loquitur instruction as requested by Oilman.
FALSUSINUNO
Oilman argues that the trial court erroneously exercised its discretion when it refused to submit a falsus in uno instruction to the jury. That instruction, Wis JI — Civil 405, provides:
*658If you become satisfied from the evidence that any witness has willfully testified falsely as to any material fact, you may, in your discretion, disregard all the testimony of such witness which is not supported by other credible evidence in the case.
Oilman reasons that because Dr. Berridge had testified falsely, the instruction should have been given.
The decision whether or not to give the falsus in uno instruction is within the broad discretion of the trial court. State v. Robinson, 145 Wis. 2d 273, 281, 426 N.W.2d 606, 610 (Ct. App. 1988). Such decisions will be upheld if they "are the result of a rational mental process and are reasoned and reasonable." Id. If the instructions, as given, adequately cover the applicable law, there is no error. Id.
Wisconsin's falsus in uno instruction is a derivation of the old maxim, falsus in uno, falsus in omnibus, or translated, "false as to one thing, false as to all things." See 4 JONES ON EVIDENCE § 29.12 (6th ed. 1972). This maxim is an outgrowth of the early rule that a person who was convicted of wilful perjury was not a competent witness in any other case. Id. Consequently, in older cases, the falsus in uno instruction was sometimes formulated so that, if the jury believed a witness to be lying, it must disregard that person's entire testimony. Annotation, Modern View as to Propriety and Correctness of Instructions Referable to Maxim "Falsus in Uno, Falsus in Omnibus," 4 A.L.R.2d 1077, 1081-84 (1949). The more common instruction, however, like Wisconsin's instruction, is given in a form that "permits" a jury to disregard the testimony of the witness, if it so chooses. See id. at 1078.
*659In general, the falsus in uno instruction has fallen into disfavor among the courts of this country.3 See id. "The now prevailing attitude... is one of tolerance and sufferance. The instructions labor under faint praise, and are generally regarded as of little assistance to juries." Id. (footnotes omitted). Professor Wigmore wrote the following criticism of the maxim:
It may be said, once for all, that the maxim is in itself worthless; — first, in point of validity, because in one form it merely contains in loose fashion a kernel of truth which no one needs to be told, and in the others it is absolutely false as a maxim of life; and secondly, in point of utility, because it merely tells the jury what they may do in any event, not what they must do or must not do, and therefore it is a superfluous form of words.
3A WIGMORE ON EVIDENCE § 1008 (Chadbourn rev. 1970) (footnote omitted).
In this state, a falsus in uno instruction is appropriate only in situations where a witness wilfully and intentionally gives false testimony relating to a material fact, and is not proper where there are "[m]ere discrepancies in the testimony that are most likely *660attributed to defects of memory or mistake." State v. Williamson, 84 Wis. 2d 370, 394, 267 N.W.2d 337, 348 (1978). In previous cases discussing a trial court's refusal of the falsus in uno instruction, this court and the supreme court have held that no error existed because the instruction would have been inappropriate under the circumstances. See, e.g., id. at 394-95, 267 N.W.2d at 348-49; Robinson, 145 Wis. 2d at 282-83, 426 N.W.2d at 611. In the present case, the trial judge refused to give the falsus in uno instruction. Oilman argues that the instruction should have been given because Dr. Berridge admitted to having testified falsely as to "(1) the cause of the complications of the first surgery . . . and (2) the reason he ruptured the spleen in the second surgery ...." Oilman also argues that "Dr. Berridge admitted to falsifying his testimony and a medical record on the stand."
In refusing to give the falsus in uno instruction, the trial judge concluded that the instruction should not be given because Dr. Berridge "did acknowledge [the operating report] was false." The trial court's ruling, however, only addresses the issue of the medical record and is unclear as to whether the trial judge believed that Dr. Berridge had wilfully and intentionally given false testimony.
Oilman argues that the judge erroneously exercised her discretion based upon a mistaken legal conclusion that a falsus in uno instruction is not appropriate where the witness later admits to having testified falsely. Cf. Oostburg State Bank v. United Savings & Loan Ass'n, 130 Wis. 2d 4, 11-12, 386 N.W.2d 53, 57 (1986) (reliance on an incorrect legal standard evidences an erroneous exercise of discretion). We agree that such reasoning would be *661erroneous. Thus, if the trial judge relied on such reasoning, the judge erroneously exercised her discretion in denying the instruction.4 We conclude, however, that if any such error occurred, it was harmless because the jury was given the standard instructions for credibility of witnesses and weight of evidence, see Wis JI — Civil 215,5 and Oilman's counsel was permit*662ted to fully argue any inconsistencies in Dr. Berridge's testimony to the jury.6
Under the standard jury instruction Wis JI — Civil 215, the jury is instructed that it is the sole judge of credibility of witnesses and of the weight to be given to the testimony. The jurors are to consider many factors, including a witness's bias, interest in the case, conduct, and demeanor, as well as facts and circumstances appearing in the trial. Jurors may also "take into account matters of . . . common knowledge and . . . observations and experiences in the affairs of life."
The falsus in uno instruction informs the jurors that they are allowed to disbelieve, in part or in whole, the testimony of a witness whom they believe has lied. We conclude, however, that the import of the instruction is more than adequately conveyed by the general instruction on credibility and weight of evidence.7 The *663principle embodied in the falsus in uno instruction is not unique to the law. That one might disbelieve statements of a known liar is, as a matter of common sense, a principle that applies in all aspects of daily living. Jurors, once informed of their role as the sole judges of credibility, need no further instruction on how to assess the credibility of a witness who they believe has given wilfully false testimony.
Furthermore, in closing arguments, Oilman's attorney was permitted to argue to the jury that Dr. Berridge had lied while giving testimony. Counsel made numerous references to the "fact" that Dr. Ber-ridge had "lied," and gave detailed accounts of the inconsistencies among Dr. Berridge's medical record entries, deposition testimony and trial testimony.
Thus, under the circumstances, we conclude that, even if the falsus in uno instruction might have been appropriate under the circumstances of this case, the failure to give that instruction was not reversible error because the jury was correctly and adequately informed of its general duty to assess credibility and *664weigh the evidence, and counsel was allowed to argue the inconsistencies to the jury.8
OPINION EVIDENCE OF NURSE ROOS
Oilman argues that the trial court erroneously exercised its discretion by granting Dr. Berridge's motion in limine to prohibit Nurse Roos, a witness to the surgery, from testifying to her opinion concerning his conduct of the surgeries or of his competency or qualifications as a doctor. This issue was not raised in a post-verdict motion, and thus, is not reviewable as a matter of right. See Rennick v. Fruehauf Corp., 82 Wis. 2d 793, 808, 264 N.W.2d 264, 271 (1978). We decline to address the issue.9
*665ORDER STRIKING OPINION EVIDENCE OF DR. FETHERSTON
Oilman objects to a ruling of the trial court which struck all of Dr. Fetherston's testimony of negligence as to Dr. Berridge's order to terminate antibiotics four days after the first surgery. Oilman contends that, from the fact of his poor condition at the time of the antibiotics' termination and the subsequent aggravation of his condition, the jury could infer the causal relationship between the premature discontinuation of the antibiotics and the subsequent development of the pelvic abscess.
Dr. Fetherston's testimony on the matter was as follows:
Q: Dr. Fetherston, do you have an opinion regarding the extent that antibiotics should be used after a surgery with complication such as those that occurred on Mr. Oilman on August 23rd of 1983?
A: Well, typically in an abdominal surgery without complications, it's — you know, for 48 hours antibiotics are often continued. If there are complications, depending on the complications — and spilling of bowel contents into the abdomen would be obviously a complication — so I would be concerned about the development of peritonitis or an abscess, and I would think that they would have been continued for ten days to two weeks.
MR. PETERSON [defendant's counsel]: I would move that the answer be stricken as speculative, Judge,
THE COURT: I'm going to overrule you at this point.
*666MR. HALE [plaintiffs counsel]:
Q: Doctor, in this case did peritonitis and abscesses develop in Mr. Oilman?
A: Yes, they did.
Dr. Fetherston later testified:
Q: .... Do you have an opinion as a family practitioner if it was below the standard of care as a surgeon for Dr. Berridge to discontinue those antibiotics?
A: It would be my opinion as a family physician if there was bowel spillage in the operation that antibiotics should have been continued for a longer period of time.
The trial court determined that, although Oilman had elicited opinion testimony that Dr. Berridge had ordered the premature termination of the antibiotics, and that such conduct fell below the standard of care, Oilman had not asked the question of whether the discontinuation of the antibiotics caused the abscess. Thus, the trial court ordered the remainder of Dr. Fetherston's testimony regarding the antibiotics to be stricken. Oilman contends that the ruling of the trial court evidences an erroneous exercise of discretion due to a mistaken view of the law regarding causation. See Schmid v. Olsen, 111 Wis. 2d 228, 237, 330 N.W.2d 547, 552 (1983) (erroneous exercise of discretion is shown where trial court bases its decision on erroneous view of law). We disagree.
To establish liability, a plaintiff must prove not only that the defendant's conduct was negligent, but also that the negligent conduct was "the cause in fact or a substantial factor in causing the eventual injury." *667Dettmann v. Flanary, 86 Wis. 2d 728, 736, 273 N.W.2d 348, 351 (1979). "Causation is a fact; the existence of causation is an inference to be drawn from the circumstances by the trier of fact." Johnson v. Misericordia Community Hosp., 97 Wis. 2d 521, 560, 294 N.W.2d 501, 521 (Ct. App. 1980), aff'd, 99 Wis. 2d 708, 301 N.W.2d 156 (1981). Nonetheless, "the lack of expert testimony on the question of causation results in an insufficiency of proof where the issue involves technical, scientific or medical matters which are beyond the common knowledge or experience of jurors and the jury could only speculate as to what inference to draw." Bruss v. Milwaukee Sporting Goods Co., 34 Wis. 2d 688, 696, 150 N.W.2d 337, 341 (1967).
In the present case, the causal relationship between the abdominal surgery, the fecal spill, the premature cessation of antibiotics and the abscess requires a determination that is beyond the ken of the average layperson. Oilman, therefore, was required to present expert testimony proving cause, but he failed to do so. Thus, we find no error in the court's striking of the remaining testimony.
EXCLUSION OF BOARD OF INQUIRY CONCLUSIONS
During his deposition, Dr. Berridge was questioned about his knowledge of proceedings before the board of inquiry of St. Michael's Hospital in the Fall of 1983. The subject of the inquiry was, at least in part, Dr. Berridge's first surgery on Oilman on August 23, 1983. In his deposition testimony, Dr. Berridge revealed that he possessed a copy of a letter describing the conclusions of the board that had been written by the board's chairperson and forwarded to the hospital's *668chief of staff. The letter allegedly stated that the conclusion of the board of inquiry was to require that Dr. Berridge submit to a complete physical and mental examination. More than three years after that deposition testimony, Oilman requested that the court compel Dr. Berridge to produce the letter. The court denied that motion.
The record on appeal contains the motions of counsel, the briefs in support of such motions, and the trial court's order. The record does not contain the transcripts of the hearing on the motion, in which the trial court made its ruling, and presumably, set forth its reasoning. The trial court's order states that Dr. Ber-ridge did not have to produce the letter, that the letter fell within the protections granted by sec. 146.38(2), Stats., and that Dr. Berridge had not "waived" or "released" the information under sec. 146.38(3).10 *669Oilman contends that the trial court's ruling constitutes reversible error for two reasons.
Oilman first argues that without examining the letter, or hearing any evidence regarding its nature, the court did not have sufficient evidence to rule on the motion for a protective order.11 Because we have no record of the motion hearing or the court's ruling, we are unable to determine what the trial court did, or did not do to ascertain the nature of the letter. Nonetheless, the parties seem to agree that the trial court did not examine the letter in camera. Oilman argues that without an in camera inspection of the document, the trial court could not have properly exercised its discretion in denying his motion to compel.
This court has previously held that where discovery requests "do not, on their face, request materials and information which fall under the protection of sec. 146.38," but the party upon whom the discovery request was made, nonetheless, objects to producing *670the document, an in camera inspection of the documents should be utilized to sort out privileged materials. State ex rel. Good Samaritan Medical Ctr. v. Moroney, 123 Wis. 2d 89, 91-92, 365 N.W.2d 887, 889 (Ct. App. 1985). Unlike the request in Moroney, however, Oilman's motion to compel discovery did, on its face, demand information that was clearly protected by sec. 146.38, Stats. In that motion, Oilman requested an order compelling production of a letter identified only as "the 1983 letter outlining the conclusions reached by the Board of Inquiry." Under sec. 146.38(2), conclusions of a review board are confidential, and are not to be disclosed except as specifically provided in that statute.12 Thus, because Oilman's motion to compel, on its face, requests a particular document identified only as one containing the conclusions of the Board of Inquiry, the trial court did not err in denying that motion without an in camera inspection of the document itself.
Oilman's second argument is that the trial court erred in ruling that Dr. Berridge's voluntary disclosure of the contents of the letter did not waive the protections offered by sec. 146.38, Stats. Although rulings on discovery motions are within the trial court's discretion, the court's ruling on this issue involved statutory interpretation, which presents a question of law that this court reviews de novo and without deference to the decision of the trial court. Franzen v. Children's Hospital, 169 Wis. 2d 366, 376, 485 N.W.2d 603, 606 (Ct. App. 1992).
*671The statute provides that information acquired in connection with the review of the services of a health care provider, and records kept by the reviewing organization, cannot be disclosed "except as provided in sub. (3)." Sections 146.38(lm) and (2), Stats. Subsection (3)(b) provides that the health care provider can consent to the release of such information. Oilman argues that Dr. Berridge's deposition testimony in response to questions regarding the conclusions of the board of inquiry was, in effect, his "consent." Oilman cites no authority for this proposition. We reject the argument that Dr. Berridge implicitly consented to the disclosure of the letter. The record clearly indicates Dr. Berridge's explicit refusal to produce the document.
Alternatively, Oilman argues that, because the letter containing the conclusions of the board of inquiry had been addressed to a hospital vice president who was not a member of the board of inquiry, the statutory protection was "destroyed." Oilman relies on State v. Dalton, 98 Wis. 2d 725, 732, 298 N.W.2d 398, 401 (Ct. App. 1980), for the proposition that a "privilege" can be destroyed by subsequent disclosures to third parties. Dalton dealt with the statutory privilege between husband and wife under sec. 905.05(1), Stats. The statutory privileges provided in chapter 905 can be waived by the voluntary disclosure or consent to disclosure of the privileged communication. Section 905.11(1), Stats. By contrast, sec. 146.38, Stats., contains no provision for waiver by disclosure. Section 146.38 provides that the only exceptions to the disclosure rule are contained within the statute itself. Accordingly, expressio unius est exclusio alterius — "the expression of one thing is the exclusion of *672another." Black's Law Dictionary 581 (6th ed. 1990). See also Gottlieb v. City of Milwaukee, 90 Wis. 2d 86, 95, 279 N.W.2d 479, 483 (Ct. App. 1979). Thus, because the list of exceptions found in sec. 146.38 does not provide for the loss of confidentiality due to disclosure to third parties, we conclude that no such waiver exists under the statute.
We therefore affirm the trial court's denial of Oilman's motion to compel disclosure of the letter.
Finally, Oilman requests a new trial in the interest of justice. See sec. 752.35, Stats. His argument merely restates the issues presented on appeal. Because we have found no reversible error on those issues, we reject Oilman's request for a new trial in the interest of justice.
By the Court. — Judgment affirmed.