The skins of animals, however prepared to receive writing, were cut into strips and, at the first, were fastened together in a continuous roll--sometimes to the extent of a hundred feet or more in length. The last strip of the manuscript was attached to a reed or stick, called the _umbilicus_, around which, somewhat as a mounted map or a window-shade, the whole length was rolled. It is to be remembered that the first books, whether of parchment or papyrus, were not made up of leaves and pages but of rolls--were, literally, "volumes." These rolls were written usually on but one side of the material, in narrow, cross-wise columns. A volume was unrolled and re-rolled, as read; was "closed" by rolling it up around the umbilicus; and was "fastened" by tieing it with a string--was often "sealed" with wax. [In the book of Revelation (5:7-9) there is portrayed the breaking of the "seals" in order to read the contents of the book.] The Hebrew scriptures, used in the synagogue worship, were "books" of this form, as likewise was the "book" referred to in the fortieth psalm, "In the volume of the 'book' it is written of me." It is not determinable, either at what time or for what reasons, the change was made in the form of the manuscript from the continuous roll to the book of separate leaves. As we have noted, it is the fact that "necessity is the mother of invention," the world over and throughout history. It is also the fact that the improvements of inventions have ever been the order of development, inasmuch as few inventions, if any, in any age or realm, have ever come into existence full-grown--are other than improvements, and sometimes after long and patient and untiring persistence, upon earlier and it may be crude and imperfect originals. Thus the improvements in the preparation of skins and papyrus, making it possible to use both sides of the materials, doubtless facilitated the transition to the book of leaves and pages. This change was gradual and was furthered or even occasioned it may be by utilitarian demands, or was prompted by economy in the use of book-making materials which were constantly enhancing in value. Professor Dobschütz has this to say concerning the change from the papyrus roll to the parchment book: "The use of this latter form seems to originate in the law schools; the codex, or parchment book, is at first the designation of a Roman law-book. But at an early date the Christian Church adopted this form as the more convenient one and gave it its circulation."[25] The fact that parchment and vellum increased in cost and became less and less available as writing material led to the custom, during periods of the Middle Ages, of transcribing one work over another, and after the earlier had been obliterated. This "composite" writing was a "palimpsest," called, technically, a _codex rescriptus_, and many times obscured or destroyed an ancient and valuable production. Some of these "palimpsests," though fragments