By MOTOKO RICH


For more than 500 years the book has been a remarkably stable entity: a coherent string of connected words, printed on paper and bound between covers.

But in the age of the iPhone, Kindle and YouTube, the notion of the book is becoming increasingly elastic as publishers mash together text, video and Web features in a scramble to keep readers interested in an archaic form of entertainment.

For instance, Simon & Schuster, the publisher of Ernest Hemingway and Stephen King, worked with a multimedia partner to recently release four “vooks,” which intersperse videos throughout electronic text that can be read - and viewed - online or on an iPhone or iPod Touch.

And in early September Anthony E. Zuiker, creator of the television series “CSI,” released “Level 26: Dark Origins,” a novel - published on paper, as an e-book and in an audio version - in which readers are invited to log on to a Web site to watch brief videos that flesh out the plot.

Some publishers say a multimedia hybrid is necessary to lure modern readers. But reading experts question whether altering the parameters of books ultimately degrades the act of reading.

“There is no question that these new media are going to be superb at engaging and interesting the reader,” said Maryanne Wolf, a professor of child development at Tufts University in Massachusetts. But, she added, “Can you any longer read Henry James or George Eliot? Do you have the patience?”

The most obvious way technology has changed the literary world is with electronic books. Over the past year devices like Amazon’s Kindle and Sony’s Reader have gained in popularity. But the digital editions displayed on these devices remain largely faithful to the traditional idea of a book by using words - and occasional pictures - to tell a story or explain a subject.

The new hybrids add much more. In one of the Simon & Schuster vooks, a fitness and diet title, readers can click on videos that show them how to perform the exercises. A beauty book contains videos that demonstrate how to make skin-care potions.

Simon & Schuster is also releasing two digital novels combining text with videos a minute or 90 seconds long that supplement the story line.

In “Embassy,” a short thriller about a kidnapping written by Richard Doetsch, a video clip that resembles a newscast reveals that the victim is the mayor’s daughter.

“Everybody is trying to think about how books and information will best be put together in the 21st century,” said Judith Curr, publisher of Atria Books, the Simon & Schuster imprint that is releasing the electronic editions in partnership with Vook, a multimedia company.

The children’s division of Harper- Collins recently released the first in a young-adult mystery series called “The Amanda Project,” and has invited readers to discuss clues and characters on a Web site. Some of the reader comments may be incorporated into minor characters or subplots.

Jude Deveraux, a popular romance author, said she envisioned new versions of books enhanced by music or even perfume. “I’d like to use all the senses,” she said.

Some authors scoff at the idea of mixing the two mediums. “As a novelist I would never ever” allow videos to substitute for prose, said Walter Mosley, the author of “Devil in a Blue Dress” and more than 20 other books.

“Reading is one of the few experiences we have outside of relationships in which our cognitive abilities grow,” Mr. Mosley said. “And our cognitive abilities actually go backwards when we’re watching television or doing stuff on computers.”