Gore wins by a head - and more

Perhaps the most gratifying thing you can say about the Hayward Gallery's new show, "Spectacular Bodies", is that there is a moment in it when you feel a genuine sense of shock. The second part of the exhibition, called "The Divine Machine", is built around cases full of écorché figures, images of male and female criminals flayed on the anatomist's table after execution and then forced to adopt poses from classical art.

Perhaps the most gratifying thing you can say about the Hayward Gallery's new show, "Spectacular Bodies", is that there is a moment in it when you feel a genuine sense of shock. The second part of the exhibition, called "The Divine Machine", is built around cases full of écorché figures, images of male and female criminals flayed on the anatomist's table after execution and then forced to adopt poses from classical art.

Thus, the cheerily named Smugglerius by William Pink is cast from the body of a condemned smuggler whose limbs had been pressed, post mortem but pre-rigor mortis, into the attitude of The Dying Gaul. Another miscreant, even more unfortunate, is condemned to spend all eternity as a Quirinale horse-trainer. Since the horse in question isn't included in the piece, the flayed man appears to be dancing to some kind of noiseless rumba beat. A dignified posterity it is not.

It is not only modern eyes that are struck by the cruel and unnatural nature of this punishment. One of the first works you see on entering "Spectacular Bodies" is Rembrandt's The Anatomy Lesson of Dr Jan Deijman, on loan to the Hayward from the Amsterdams Historisch Museum. If the work seems familiar, then it may be because the foreshortened cadaver, whose sticky-pink brain is being exposed by the eponymous medic, bears a strong resemblance to Mantegna's dead Christ. Far from endorsing scientific method, The Anatomy Lesson equates it with original sin.

Gory though all of this is, though, the goriest is yet to come. Follow the écorché trail past the variously dismembered waxworks by the 18th century anatomical model-maker, Clemente Susini - Head and body of a young woman with muscles and blood vessels is particularly unappealing - and you will end up at a piece of such extraordinary bloodiness that its sole purpose seems to be to be bloody. Which is precisely what it is.

The work, A Necessary Change of Heart, is not by Susini at all, but by a contemporary artist called John Isaacs. Cast from its maker's own body, Isaacs' waxwork is not just shocking because it is slicked with unpalatably real-looking acrylic blood. The work's true shock-value lies in the fact that it makes explicit the cruelty implicit in all those écorché gladiators and dismembered wax models around it. There's no denying that Susini's bisected women are artfully made, their bloodless lips and sightless eyes shaped by the beautifying ideals of the late Italian Baroque. Even Rembrandt, for all the moralising of his Anatomy Lesson, cannot resist the painterliness of soft tissue, the play of light on an exposed dead brain.

The real sickness of all this, though, is not that artists can find dreadful things beautiful - terribilitá has been a quality of art since the Renaissance at least - but that they can do so so covertly, dressing up a gratuitous taste for the aesthetics of gore in the guise of forensic disinterest. By making a work that is shamelessly (even joyously) gory, Isaacs's Change of Heart brings you up short. It makes you wonder about the motivation behind everything else in "Spectacular Bodies", from Leonardo's Muscles of the Shoulder and Spine to the glass vertebrae - commissioned, like Isaacs' wax man, specially for this show - of Katharine Dowson's Pia Mater.

But Isaacs' flayed self-portrait raises another question as well: namely, exactly what it is doing there. By dotting contemporary works among the Rembrandts and Susinis - a Hirst-ish vitrine of pickled flowers from Marc Quinn here, a pair of talking bulls' testicles in a bell jar by Tony Oursler there - the Hayward's curators presumably want us to feel that there is some kind of eternal impulse at work. The trouble is that, for the life of me, I can't imagine what that impulse is meant to be.

There are all kinds of potentially interesting things to be thought about in "Spectacular Bodies": the way in which anatomical artists work from the inside outwards, for example, or the play-off between personal expression and taxonomic exactitude in body-based art. The trouble is that no-one at the Hayward seems to be willing to let you in on the secret of what those interesting things might be. The curators of "Spectacular Bodies" certainly can't be accused of being heavy-handed. In fact, unless you lash out on the catalogue and read it cover to cover, you may wander out of the show wondering just what it is that you have just been looking at, and why.

'Spectacular Bodies: The Art and Science of the Human Body from Leonardo to Now': Hayward Gallery, London SE1 (020 7960 4242) to 14 January, 2001