FRANCIS BACON ONCE said that he wanted to create images which communicate directly with the nervous system. He was preceded in this by Goya. No other artist needles away so remorselessly at our sense of the tragic. This may seem obvious in his Disasters of War etchings (which famously record man's inhumanity to man), but a similar effect can be found in his paintings as well. It is much less expected, for instance, in his portrait of the four-yearold son of the Count of Altarnira, but it is there. Beguilingly sweet in his red silk outfit with its silvery-white sash, the child holds a string which is attached at the far end to the leg of his pet 1nagpie. Near by, two crouching cats stare at the bird with murderous intent, while close at hand is a cage of finches , also, it would seem, in imminent danger.