be asserted,[1] On the other hand, the Supreme Court of Michigan expresses its preference of the opposite rule, laid down by an earlier case decided in New York,[2] and, accordingly, holds that the privilege, having once been waived, may be again asserted upon a subsequent trial of the case.[3]
Expert Evidence.
It has been shown that, as a general rule, opinions are incompetent, and that the witness will not be permitted to express them in testifying. This rule is subject to certain exceptions, one of which is particularly important and includes all of that class of evidence known as expert.
This class of evidence, falling under the head of an exception, is admissible in a certain class of cases only; that is, in those cases where the subject-matter of the issue involves questions outside of the range of ordinary knowledge and experience, and where one without particular experience or study would be incapable of forming a correct judgment thereon. The opinions of an expert witness are admissible, to use the words of Mr. Chief Justice Shaw, "because a man's professional pursuits, his peculiar skill and knowledge in some department of science, not common to men in general, enables him to draw an inference, where men of common experience, after all the facts proved, would be left in doubt."[4]
Whenever the physical condition of one becomes pertinent in any suit, it will be perceived that the facts presented will probably be such that questions will arise which the jury will be incapable of comprehending, and that the assistance of a physician will be proper, if not necessary, to their comprehension.
The evidence of medical experts has constituted a very important branch of expert evidence; in fact, it seems that the earliest recorded instances of the giving of this class of evidence were those where medical expert evidence was produced. About the middle of the fourteenth century, a case is reported in England where, after failure of the justices to determine from inspection whether an injury constituted mayhem, called to their assistance surgeons from London
