You can tell whether a book is sewn by looking for the centrefold of a gathering of leaves. In my copy of the Middle Liddell the first centrefold is at pages 8/9. Open the book right open as far as possible and look down the very centre of the centrefold of these pages. If the book is sewn there will be a discontinuous line of thread visible. Perfect-bound books (i.e. books bound only with adhesive) are not bound into gatherings (known as "sections") at all, but are simply single sheets of paper glued down the spine edge. This style of binding is cheap and cheerful but rarely makes a book suitable for long term use.
