Jon Stewart, who already had a reputation for lobbing word grenades at media personalities and outlets that displease him, this week delivered one of the most sustained criticisms of Fox News ever heard on Fox News.

That network, lambasted by many on the left as an arm of the conservative movement, is a “cyclonic perpetual emotion machine” that has “taken reasonable concerns about this president and this economy and turned it into a full-fledged panic about the next coming of Chairman Mao,” Mr. Stewart told Bill O’Reilly of Fox.

Parts of the interview were shown on Wednesday and Thursday evenings on Fox News’s most popular program, “The O’Reilly Factor,” and were widely praised by television critics. But Mr. Stewart had a lot more to say about Fox in the portions of the interview that were edited out of the television broadcast.

The exchanges are notable because Mr. Stewart, the host of “The Daily Show” on Comedy Central, has occasionally strayed beyond his comedy roots into serious media criticism and drawn great attention for doing so. On “Crossfire” on CNN in 2004, he claimed the left-right debate format was “hurting America,” three months before the program was canceled. Last year he took aim at CNBC for being Wall Street cheerleaders, telling Jim Cramer, the host of its “Mad Money” program, that “the financial news industry is not just guilty of a sin of omission but a sin of commission.”