If you're any kind of aficionado of phlegm, mucus, pus, and related body waste management -- and who among us is not? -- you've got to admire the tenderhearted obsessiveness with which the filmmaking Farrelly brothers, Peter and Bobby, pursue grossness as the great social leveler. The potent Farrelly oeuvre triumphs not only because the filmmakers appreciate that Everyone Poops (a truth persuasively defended in the cult hit 1993 children's book of the same name) but because they know that everyone is fascinated by the product.
Until now, though, the Farrellys have saluted body fluids from the outside in: Millions heard the efforts of Jeff Daniels on the toilet in ''Dumb and Dumber,'' and saw the effects of unusual hair gel in ''There's Something About Mary.'' But millions more (remembering Woody Allen dressed as a sperm) have probably wondered: What are gross body functions like from the inside out?
Osmosis Jones goes deep and weird for an answer, into the molecular structure of the poorly tended flesh of a sedentary shlub named Frank (Bill Murray). And you've never seen such fantastic, in your face rot. Frank -- mourning the death of his wife by gorging on junk food, apparently in the hope of joining her sooner than later -- is as grungy a specimen of middle aged decay as can appear on screen without frightening the populace. And Murray is truculently alive with mange and molt made even more putrid by the blotched out quality of Mark Irwin's cinematography.
Frank is a walking, hacking cough, a scabby man whose noxious eruptions (pimples, vomit, et al.) are tolerated only by his nearest and dearest: his marginally more evolved friend (Chris Elliott), his nutritionally correct daughter (Elena Franklin), and her teacher (Molly Shannon). And eventually, the purulent outer Frank succumbs to sickness.
That's when the inner Frank comes alive, as ''Osmosis Jones'' crazily shifts styles, becoming a fanciful animated cartoon slash hygiene lesson about viruses and antibodies, blood cells and cold capsules, all of them fighting for dominance in an interior metropolis called the City of Frank. Raquel Welch in ''Fantastic Voyage'' never faced anything so dizzying as the mad jumble of this story, written by Marc Hyman and voiced by such vitamin boosted stars as Chris Rock (as Osmosis Jones himself, a white blood cell with ambitions of being a superhero), Laurence Fishburne (as a nasty virus), and David Hyde Pierce (as the personification of fussy, precise, time released cold relief).
''Osmosis Jones'' oscillates between streaky black comedy and sanitary instruction (as well as between crude live action and elegant animation) like a patient with a fever, and viewer tolerance may similarly run hot and cold. But there's this to say in favor of the Farrellys' germ warfare: In a business where one hand is always washing the other, anyone who has ever popped a zit has got to admire the boys' clean ability to squeeze new material out of old places.