The phrase "picture book" is commonly used to describe a book,
most often written for children,in which the content, whether a
story, an alphabet, or a nursery rhyme, to name just a few
possibilities, is conveyed through the use of words and pictures
in combination or through pictures alone. A picture book differs
from an illustrated book in that the pictures it contains form
an essential part of the structure of the book. Illustrations
are supplements to a work that can stand on its own. Due to
physical factors in the bookbinding process, picture books are
conventionally 32 pages long. Picture books, thus defined, are a
relatively new form of book, originating in the early twentieth
century. Wanda Gag is widely considered to be a major innovator
in the development of picture books. The formula for illustrated
books had been to show text on the left page and pictures on the
right page, side-by-side, without combining them. In Millions of
Cats, Gag mixed up the order of the pages of pictures and text,
combined