In Illinois, a witness may, to test his knowledge, be cross-examined as to his reading of particular authors upon the subject, and as to whether reputable writers do not entertain certain views upon the subject. Paragraphs from standard authors, treating of the disease in question, may be read to the witness, and he may be asked if he agrees therewith, as one of the means of testing his knowledge; but care should be taken by the court to confine such cross-examination within reasonable limits, and to see that the quotations read are fairly selected so as to present the author’s views. Mr. Rogers questions the wisdom of this decision [248]. The witness, however, cannot read from a scientific work in his examination in chief, though he be an expert and agree with the views expressed by the author [249]. Nor can a passage from a book be got before a jury as evidence in an indirect manner, when it cannot be read to them. So it was decided where a medical man was asked if he was acquainted with a certain book; he replied, that he had heard of it, but had not read it. He was then asked |101| whether it was considered good authority, and he said it was. He was then asked to read a certain paragraph; this he did, and was re-called. Counsel then read from the book the same paragraph and asked if such a case as that stated was reported. Held to be error [250]. And in Ontario it has been held improper to ask medical witnesses, on cross-examination, what books they consider best upon the subject in question, and then to read such books to the jury; but they may be asked whether such books have influenced their opinion [251].