I respectfully dissent.
*80It is undisputed that the claimant worked in the coal mines of defendant, where a silica hazard is known to exist, from April, 1929 until June, 1955. At that time, he ceased working because of disability and never worked again. He was concededly suffering from silicosis in 1963, and that condition caused his death in 1964.
The sole question before the Board was whether the claimant became totally disabled from silicosis within four years from the date of his last employment with the defendant, on June 4, 1955.
Dr. Richard P. Jahnig, a specialist in tubercular and related diseases, testified that, on the basis of physical examinations he conducted in 1963, the claimant had become disabled some eight years earlier from silicosis. Dr. Jahnig stated:
“A. ... I feel definitely, from the cases we have seen up there and previous similar cases, that his [condition] had to exist for some years prior to his admission.
“Q. In the particular case of Mr. Lowery, how long had this silicosis endured?
“A. At least ... it was possibly eight to ten years prior.
“Q. Can you give an estimate of the period of time that the condition became so extreme that it became disabling?
“A. Some length of time, eight years ago. ... It dates back to 1955 in our medical history.
“Q. Is it your opinion then Doctor that Mr. Lowery, your diagnostic opinion, that Mr. Lowery had had a condition of silicosis and silieotuberculosis since around 1955, 1956?
“A. It would be my opinion, yes.”
*81The doctor’s testimony remained unshaken on cross-examination.
Doctor Sydney Safron, the claimant’s attending physician, fully corroborated this testimony. Dr. Safron did testify, as the majority notes, that the claimant initially sustained a heart attack in 1955, and was treated for coronary insufficiency, myocardial infarction, and angina pectoris. However, Dr. Safron went on to state that he had never looked for silicosis in 1955, because he had no facilities with which to make such a diagnosis at that time. He candidly told the Referee that, in light of what he had since learned, the claimant’s “disability was caused by emphyzema and silicosis which we did not know existed.”
The defendant introduced no evidence whatever. Nonetheless, the Workmen’s Compensation Board dismissed the petition, finding that claimant “did not become totally disabled . . . within the time and requirements of §301 (c) of said Act.” To reach this conclusion, the Board wholly rejected the uncontradicted, fully corroborated testimony of the claimant’s medical witness, Dr. Jahnig, and substituted its own judgment for that of the medical expert.
This is not a case in which the doctor’s testimony was rejected because it was “weak and uncertain” or because it was “indefinite and inconsistent.” Cf. Brasacchio v. Pennsylvania Highway Department, 208 Pa. Superior Ct. 212, 222 A. 2d 418 (1966). The sole reason offered by the Board for disregarding the competent, uncontradicted, and corroborated medical testimony of Dr. Jahnig was that it was “not credible.”1
It is true that the Board is not required to accept the uncontradicted testimony of any witness, at least where it is not corroborated. Peron v. Phoenix Park *82Coal Co., 202 Pa. Superior Ct. 495, 198 A. 2d 370 (1964). In this case, however, the Board has exceeded even that authority, and wholly disregarded uncontradicted testimony which was substantiated by another, disinterested witness.
In my view, this case demonstrates that the Board’s discretion as the “ultimate fact-finder” must be qualified by its obligation to deal rationally and coherently with the evidence before it. To reject the testimony of Dr. Jahnig, on this record, by characterizing it as “competent but not credible” seems to me so arbitrary as to require corrective action by this Court. The Board’s terse and cryptic language, if approved by us, renders impossible any meaningful review of its action on appeal.
While I acknowledge the Board’s power to reject the testimony in question, I believe it has the duty to explain precisely why, on this record, the medical specialist’s testimony was “not credible.” The record should show with some particularity the Board’s reasons for rejecting the only evidence presented in a difficult and complex area, where the Board’s own expertise is not especially relevant, and when, after all, it did not itself observe the demeanor of the witnesses. In the language of Mr. Justice Frankfurter, “[T]he orderly functioning of the process of review requires that the grounds upon which the . . . agency acted be clearly disclosed and adequately sustained.” S.E.C. v. Chenery Corp., 318 U.S. 80, 94 (1943); cf. 2 Davis, Administrative Law (1958) §16.12, and 2 Larson, Workmen’s Compensation Law (1961) §79.54.
I am especially concerned to see an explanation of the Board’s action in this case, because there is a substantial danger that it has applied a rule never specifically approved by this Court. That rule would exclude from consideration the testimony of an expert medical witness as to the date of the commencement of claim*83ant’s disability, where the date is prior to the doctor’s first examination of the claimant. If the Board is indeed relying on such a rule, it should say so, and subject the rule to judicial scrutiny.2
The real difficulty here is that we can discern nothing whatever from the Board’s opinion. To acquiesce in its disposition of this case on the ground that “it is for the Board as the final fact-finding body to determine from all the evidence whether claimant has sustained the burden resting upon him,” seems to me to be an abdication of our judicial responsibility.
1 would remand the record to the Board for a more precise explanation of its reasons for rejecting the claimant’s petition.
Although our Court now characterizes Dr. Jahnig’s testimony as “indefinite and equivocal” and “based on speculation and conjecture,” the record shows that the Board made no such finding.
Judge Flood, dissenting in Obzut v. Philadelphia & Reading Coal & Iron Co., 199 Pa. Superior Ct. 289, 293, 181 A. 2d 381 (1962), did come to grips with this question, although the majority in that ease did not. H’e flatly and persuasively rejected the contention that the Board could reject expert medical testimony on the ground stated above.