ead and
put over the end of the old, and, on being pulled tight, the old
thread should slip through, as shewn at B. The convenience of this
knot is, that by its use a firm attachment can be made quite close up
to the back of the book. This is a great advantage, as if the knot is
made at some distance from the back, it will have to be dragged
through the section two or three times, instead of only once. The
knot, after having been made, must be pulled inside the section, and
remain there. Considerable judgment is required in sewing. If a book
is sewn too loosely, it is almost impossible to bind it firmly; and if
too tightly, especially if the kettle stitches have been drawn too
tight, the thread may break in "backing," and the book have to be
resewn.

One way to avoid having too much swelling in the back of a book
consisting of a great many very thin sections is to sew "two sheets
on." In this form of sewing two sections at a time are laid on the
sewing-frame. The thread is inserted at the "kettle stitch" of the
lower section, and brought out as usual at the first cord, but instead
of being reinserted into the lower section, it is passed into the
upper one, and so on, alternately passing into the upper and lower
sections. This will give, if there are five bands, three stitches in
each section instead of six, as there would be if the sewing were
"all along," lessening the thread, consequently the swelling by half.
It is usual to sew the first and last few sections "all along."

The common method of sewing is to make saw cuts in the back, in which
thin cords can be sunk, and the thread merely passes behind them and
not round them, as in flexible sewing. This method, although very
quick and cheap, is not to be recommended, on account of the injury
done to the backs of the sections by the saw, and because the glue
running into the saw cuts is apt to make the back stiff, and to
prevent the book from opening right to the back. Indeed, were a
sawn-in book to open right to the back, as it is expected a
flexibly-sewn book will do, showing the sewing along the centre of
each section, the saw marks with the band inserted would show, and be
a serious disfigurement.

Mediaeval books were usually sewn on double cords or strips of leather,
and the headband was often sewn at the same time, as shown at fig. 32,
A. This is an excellent method for very large books with heavy
sections, and is specially suitable for large vellum manuscri