The weight of authority seems to sustain the doctrine that medical and scientific books, even though they be standard authorities on the subjects to which they relate, including the U. S. Pharmacopoea, are not admissible in evidence, although the decisions in the various jurisdictions are not uniform. Books of science by statute in some states have been made competent evidence.

Where, however, an expert has testified that he based his opinion upon a certain medical or scientific book, such book may be read in evidence to contradict his opinion.