It is admitted by all writers on typography that block-books of both classes were made before and after the invention of typography. That they were manufactured in large quantities by many printers, and in many cities or towns, during the fifteenth century, does not admit of doubt. It is claimed by one bibliographer that there are eight editions of the _Ars Moriendi_; by others, that there are six editions each of the _Bible of the Poor_ and of the _Apocalypse_, and four of the _Mirror of Man’s Redemption_. In some instances, the so-called later editions are reprintings, with slight alterations, of the same blocks that were used for the first edition; in other instances, the later editions were printed from blocks newly engraved. The number and variety of the editions are proof that there must have been a very large demand for the books; the alterations in the engravings are presumptive evidence of [p195] repairs to blocks badly worn by long use; the newly engraved blocks are evidently the replacement of a suite completely worn out; an edition different from the others in design may be accepted as the work of a rival or competing printer. The few block-books known in the seventeenth century were regarded by bibliographers as prejudicial to the claims of contestants for the honor of the invention of typography. They were annoying facts which could neither be rejected nor accepted without hurt to favorite theories. There was a disposition on all sides to belittle them in number as well as in importance. The first writer who called attention to their value as relics could describe but nine block-books. Sotheby, writing about them in 1858, described in the _Principia Typographica_ twenty-one block-books—not different editions of a few books, but twenty-one distinct works. Even with these additions, the list cannot be considered complete: it is possible that more will yet be found, but it is certain that many have been irretrievably lost.