In his unpublished satire An Island in the Moon, the artist and poet William Blake writes of a figure named Steelyard the Lawgiver, sat at his table, reading through his books. He recalls to himself a quotation from St. Jerome, the early Christian priest whose life was a popular subject for mediaeval artists. ‘Says Jerome happiness is not for us poor crawling reptiles of the earth. Talk of happiness & happiness! It’s no such thing.’ Jerome, an early Christian theologian, had experienced a vision following a prolonged sickness, and subsequently devoted himself to an ascetic life, preaching a puritan ideology of forgoing pleasures of the flesh.

Although never printed, the satire marked the beginning of a change in Blake’s writing. Blake experienced visions, and developed from them a deeply symbolic understanding of the world, where his mystical experiences and the religious stories he cherished came to contextualise the period he was living in: one of fast social change, urbanisation, and industrialisation, and the emergence of a cruel, back-breaking capitalist order. He became a radical voice for the complex and even sacred human at a time when supposedly rational ideologies, both intellectual and political, were reducing humans to mere tools. He railed against the dehumanising brutality of the Industrial Revolution, and, despite being hopeful about the French and American Revolutions, became disenchanted with what he saw as a system that simply swapped monarchism for mercantilism.

Despite dying largely unrecognised and in poverty — his collection of poems Songs of Innocence and Experience sold fewer than thirty copies in his lifetime — Blake is today regarded as one of the most important artists of the period, with the rare honour of a room dedicated to his work at Tate Britain. Currently on display is his painting The Ghost of a Flea, a wonderful example of both his draughtsmanship and his understanding of the world. In it a grotesque (if tiny) muscular monster strides across a stage, or perhaps a windowsill, the cup of an acorn gripped between its slender, sharp fingers. This flea appeared in a vision to Blake; the limit between imagination and image so porous that they become the same, or, as Alan Moore said of the painting, the belief that ‘the world of ideas is every bit as real as the material world that surrounds us’.

Blake frequently gave abstract ideas material forms; the flea he encountered in his vision told Blake himself that fleas contain the souls of the bloodthirsty and greedy. Blake had already pitched himself against the early manifestations of capitalism in his attacks on the ‘mind-forg’d manacles’ of London and its first factory, the ‘dark Satanic mills’ of the Albion Flour Mill where ‘all the Arts of Life they changed into the Arts of Death’. Here, though, the embodiment of greed is resurrected not in brick, but in the muscular flea’s frame, violent but tiny, an indicator of its moral stature.

This idea of the allegorical use of an animal to examine how bodies are understood under capitalism can be seen in the work of Jesse Darling, whose recent show, also at Tate Britain, used a hagiographic tale about St. Jerome to question the same imperious forms of knowledge that Blake attacked. In the story a lion, who has got a sharp splinter stuck in his paw, encounters St. Jerome. Rather than attacking the lion, the saint instead removed the splinter, and nursed the lion back to health.

The lion features prominently in Darling’s show, both in drawings and in two sphinx-like sculptures who guard the gallery’s door, one ball-gagged and the other hooked up to an IV drip. The lion is a self-portrait of the artist as a medical patient, whose boldness has been curtailed by injury and so now has to bring itself under the authority of St. Jerome, and the empirical forms of knowledge he represents.

In another sculpture boxes of files are stored in vitrines — the traditional way to organise and display artefacts within the sort of museums that aimed to categorise, control, and quarantine objects from other, non-Western cultures — but the vitrines themselves stand on buckled legs, unable to hold their weight or function ‘properly’. The work undermines the authority upon which the Tate stands, but does so with a sort of slapstick humour. Repurposed medical equipment — crutches, prosthetics, and straps — are turned into sculptures of vulnerable survival; like Blake’s Flea, they embody the critical ideas they hold about the medical industry, and the way it understands the bodies it either treats, or does not treat. Separated by 200 years, the work of Blake and Darling together rhymes; it uses the energy that Blake so treasured as the body’s ‘eternal delight’ to make a stalwart defence of the messy and imperfect human in the face of the cruel absolutism of capitalism’s supposed rationality.