An illustrational form tells you through the intelligence immediately what the form is about, whereas a non-illustrational form works first upon sensation and then slowly leaks back into the fact.
The only way of expressing emotion in the form of art is by finding an "objective correlative"; in other words, a set of objects, a situation, a chain of events which shall be the formula for that particular emotion; such that when the external facts, which must terminate in sensory experience, are given, the emotion is immediately evoked.
The fact that we can become accustomed to anything, however disgusting at first, makes it necessary to examine carefully everything we have become accustomed to.