(_e_) Every book-packet must be sent either without a cover, or with one open at the ends or sides, in order that the contents may be examined if it be thought necessary. For greater security, it may be tied round the ends with string, though each postmaster is empowered to remove it for the purpose of examining the packet. He will re-secure it, however, after examination. As a security against fraud, it has been found necessary to adopt precautionary measures with book-packets and newspapers: it has been demonstrated over and over again that many people will evade the Post-Office charges, cheap as they now are, if it be possible to do so.[207] When any head postmaster has grounds for suspecting an infringement of the rules of the book-post, and occasionally when he has no suspicion, he is required to open and examine packets passing through his office, in order to assure himself that the privileges of the book-post are being legitimately used. (_f_) A book-packet may contain any number of separate books or other publications (including printed or lithographed letters), photographs (when not on glass or in cases containing glass), prints, maps, or any quantity or quality of paper, parchment, or vellum. The whole of this description of paper, books, and other publications, may either be printed, written, engraved, lithographed, or plain, or the packet may consist of a mixture of any or all these varieties. The binding, mounting, or covering of books and rollers, &c. in the case of prints or maps, are allowed. In short, whatever usually appertains to the sort of articles described, or whatever is necessary for their safe transmission, may be forwarded through the post at the same rate charged for the articles themselves. (_g_) Among the general restrictions, we find the following:-- No book-packet must exceed two feet in length, width, or depth. No book-packet must contain anything inclosed which is sealed against inspection, nor must there be any letter inclosed, or anything in the way of writing in the packet of the nature of a communication, either separate or otherwise. Entries on the first page of a book, merely stating who sends it, are allowable (and even desirable in case of failure of delivery) inasmuch as they are not regarded as of the nature of a letter. Any packets found with a communication written in it (if the communication in question cannot be taken out, but forms a component part of the packet) will be charged with the _unpaid letter postage_, and then sent forward.