It has been held that a medical witness may give his opinion upon new and hitherto unknown cases whenever he swears that he can form such an opinion, even though at the same time he should admit that precisely such a case had never before fallen under his observation, nor under his notice in the books. The man of science is distinguished from the empiric in nothing more than in not relying on specifics, and also not waiting for the exact similitudes in things material and immaterial before forming a judgment as to their similarity [305]. It must always be remembered that medical men, when called as skilled witnesses, may only say what, in their judgment, would be the result of certain facts submitted to their consideration, and may not give an opinion as to |119| the general merits of the case, nor on the very point which the jury has to determine, nor on things with which a jury may be supposed to be equally well acquainted [306]. As a recent writer puts it, a medical man cannot testify as to matters not of skill in his profession, nor conclusions, nor inferences which it is the duty of the jury to draw for themselves. For instance, it was held that in a trial for murder the opinions of the surgeons as to the probable position of the deceased, when he received the blows which caused his death, are incompetent. The Judge said that he was not aware that surgeons were experts in the manner of giving blows of the description in question, or determining how the head must be placed so as most conveniently to receive them [307]. Whenever the subject matter of the enquiry is of such a character that it may be presumed to lie within the common experience of all men of common education, moving in ordinary walks of life, the rule is that the opinions of experts are inadmissible, as the jury are supposed—in all such matters—to be entirely competent to draw the necessary inferences from the facts spoken of by the witnesses [308]. Nor was the opinion of a medical witness admitted where the question, in an action for libel, was whether a physician in refusing to consult with the plaintiff had honorably and faithfully discharged his duty to the medical profession. The Judge said, the jury having all the facts before them were as capable of forming a judgment upon that point as the witness himself. Nor can an expert give an opinion of the opinion of another expert [309]. A medical man is considered an expert on the subject of the |120| value of medical services [310]. But he is not so considered when the question is one as to the amount of damages for a breach of contract not to practise physic in a certain town [311].