This is an important and disturbing book that tells the story of how, in the aftermath of the First World War, the German psychiatrist Hans Prinzhorn, working at the Heidelberg Psychiatric Clinic, amassed a collection of patients’ art, which he made famous in his ground-breaking 1922 book The Artistry of the Mentally Ill. Prinzhorn's story is set against the background of the rise of Adolf Hitler and of the Nazis’ fanatical desire to rid society of people whom they chillingly classed as possessing ‘life unworthy of life’. The Nazis viewed the works of the mad as examples of ‘degenerate’ art and identified patient-artists as suitable candidates for their mass extermination programme. The book thus follows a tragic trajectory from Prinzhorn's championing of the mentally ill as equal citizens in society to their mass murder in later decades by the Nazi regime.

Prinzhorn started collecting patients’ work from asylums throughout Germany, but extended his search to the rest of Europe, Latin America and Japan. The patients were mainly diagnosed as suffering from schizophrenia. They used a wide variety of materials – canvases, newspapers, toilet paper, wood and even chewed bread. Prinzhorn's achievement was to introduce this work to the wider world and, in particular, to artists such as Paul Klee, Max Ernst, André Breton and Salvador Dali, who all saw these patient-artists as daring innovators, uninhibited by bourgeois education or the precepts of the art academies. In the 1920s and ’30s, art inspired by insanity stood at the forefront of the avant-garde. Breton had already introduced to Surrealist circles the notion that madness was an exalted state. Under Prinzhorn's influence, madness came to be seen not only as a lens through which to make sense of the carnage of the First World War, but also as a way of exploring the hidden regions of the mind.

In his book, Prinzhorn highlighted ten patients whom he termed ‘schizophrenic masters’. This was a significant term, which he deliberately used to underline his claim that the art of mentally ill people was on an equal footing with that of the more celebrated, sane artists of the Western tradition. The author Charlie English concedes that Prinzhorn was sometimes guilty of romanticising schizophrenia, and indeed some artists, such as Breton, carried it ‘to absurd heights’ (p. 58). Nevertheless, Prinzhorn's work led to a more positive public perception of the art of the mentally ill and of the men and women who created it – a development that was to be savagely overturned with the advent of Hitler.

As a young man, Hitler had applied to the Academy of Fine Arts in Vienna, but was rejected twice. Despite this, or maybe because of it, he was left with a consuming ambition to vindicate himself on the creative stage, and he remained deeply interested in art, albeit in its more conservative and realist modes. As English observes: ‘Hitler's revolution was a cultural undertaking as much as a political one’ (p. 104). Hitler inveighed against modern art, which, from his poisonous perspective, he saw as representing the three evils of society: the Jew, the Bolshevik and the mad. By ‘purging’ society of such elements, the Nazis would build a heroic, racially ‘pure’ society. Hitler and his henchmen put on exhibitions of ‘degenerate art’, which consisted of work by modern artists and by the insane. The juxtaposition was supposed to illustrate the ‘pathology’ of modern art, which was contrasted with the ‘healthy’ realism of artists approved by the Fuhrer.

Before long, the Nazis starting introducing methods to ‘deal with’ the mentally ill. First, forcible sterilisation was brought in, and 400 000 patients underwent this procedure. In 1939, there began the first killings of patients. Carbon monoxide was used to gas patients, who were taken from asylums to remote locations where they were herded into what they thought were shower rooms, but were, in fact, places of execution. Hitler had signed the killing order on 1 September 1939. As English writes: ‘Hitler's regime was about to start something no state in history had attempted before: the industrialized mass murder of its own citizens’ (p. 179). By 1941, it is estimated that some 70 000 patients had been murdered. Even when the killing stopped, a further 130 000 patients died from starvation, neglect or from medically administered overdoses. The techniques developed to murder psychiatric patients would, of course, be used later to murder Jewish people, Roma people and other ‘undesirables’, but this time in far greater numbers.

English begins his terrible tale with the story of a patient-artist, known in Prinzhorn's book as Pohl, but whose real name, research has revealed, was Franz Karl Buhler. One of the most gifted artists in the collection, we learn later in the book that he was taken away as an old man and gassed by the Nazis. In fact dozens of the original Prinzhorn artists met a similar fate. By introducing us to Buhler at the beginning of the book and telling us about his life and art, it is all the more shocking to read of his subsequent murder. It serves to bring a deeply personal dimension to the mass horror of the Nazi regime.