Ran across this today. It's an excerpt from the (now old, but still excellent) ground-breaking book by Ann N. Martin, "Food Pets Die For." This is on Dr. Jeff Feinman's (DVM, CHV) website. For those of you who don't yet know anything/much/enough about commercial pet foods' ingredients, this (book) is one of the best places to start having your eyes opened.
"Food Pets Die For" excerpt

NOTE: Much if not all of this does NOT apply anymore to the high-quality commercial foods in the market today, ie. those that actually use human-grade, whole meat &/or organically-sourced ingredients, and natural preservatives like Vit. C, etc. However, a whole-food, raw food diet is still one of the healthiest ways to feed our furries. (the addition of organic veg's might need to be at least partially-steamed for cats, though, to mimic the partially-digested remains of same found in their prey's stomachs)

P.S. Also check out the great holistic forums Dr. Jeff provides right on his site!