Throughout the nineteenth century, doctors and epidemiologists struggled to analyse the nature of syphilis, the course that it ran, its impact on an unborn child, and the disease’s relation to mental collapse. Not until 1910 were the mysteries solved.

Syphilis could be difficult to diagnose confidently in the nineteenth century because its symptoms were identical to many non-venereal diseases; and vice versa. It is tantalising when reading Victorian fiction to wonder whether the author is deliberately hinting at a venereal origin when describing the poor health of certain characters (as an example, Mr Fairlie in The Woman in White has some of the enervation that could be one symptom). In respectable fiction, this could not be attemped overtly; but a nod to the knowing reader may well have been intended in some cases. We are likely never to know.

Dr Henry Maudsley, in an 1862 book review for the psychiatrists’ periodical The Asylum Journal, wrote his latest thinking about the etiology of the disease. Maudsley was a brilliant prose stylist, and his purple patches and fire-and-brimstone sensibility bring an odd metaphysical energy to what purported to be clinical observations.

His article reveals that what was known in 1862 was that the secondary phase of syphilis led to prostration, aching limbs, sharp head pains, skin eruptions and a sore throat. But most worrying, thought Maudsley, were the cases where the “poisoned organic system”, as he termed it, presented no external symptoms. “With such penetrating subtlety does the creeping venom steal into the most intimate and delicate processes of organic life.” This was why, he continued, the disease was apt to be mistaken for rheumatics, for example, and why cures could appear to have worked, when all that had happened was that the symptoms had gone into abeyance.

Syphilis could also be mistaken for cancer or tuberculosis, when it had formed a tumour, or “syphiloma”, he wrote, while most diseases of the brain could appear syphilitic, and vice versa. Maudsley cited epilepsy, paralysis, dementia, delirium, mania and melancholy as examples of these confusing conditions. (The anatomical illustration below dates from 1862 and purports to show degeneration of cortical matter in a person who had died suffering from general paralysis of the insane.)

In one of a number of distressing anonymous case histories, Maudsley described a supposedly cured primary syphilitic who married a virgin. Their first child was healthy, three miscarriages followed, and the fourth child was born with facial sores and sores at the mouth corners, which was declared to be syphilis that had been passed on by the husband, who, it was now clear, had not been cured after all. The husband himself had lately been complaining of headache, fever, a discharge from his nose and palate, a large node on his forehead and a thickening of the elbow joint.

Maudsley was not among the majority of medical men who believed that mothers alone transmitted syphilis to their unborn children; he blamed fathers who had led “sensuous” early lives every bit as much as mothers who had “a past”. The infants of syphilitics, if they did not miscarry, be stillborn or die soon after birth, had their nervous system permanently blighted and were predisposed to “madness” or to “idiocy”, Maudsley wrote. He suspected that many infants or young adults had died from syphilis without the cause of their illness and death ever having been established.

Maudsley was a keen follower of the published work of Continental medical men and researchers, and he cited studies undertaken in France that appeared to have identified “syphilitic epilepsy”, paralysis attributable to the syphilis virus, a syphilitic “mania” and a form of catalepsy. A German doctor, meanwhile, had identified general paralysis of the insane as the result of syphilis.

In his book review of their work, Maudsley quoted at great length Frenchmen Drs Lancereaux and Gros, who described the progress of a syphilis case approaching the final fatal phase thus: severe head pains, sometimes of a neuralgic character and with vertigo; noise in the ears, or deafness; double vision, or partial vision; partial or general paralysis; dull intellect, confused ideas, slow speech; loss of memory; sometimes great melancholy, or maniacal excitement. Towards the end, epilepsy or stroke-like attacks. Then coma; and then death.

“Is syphilis curable?” asked Maudsley. “He is a bold writer who can say positively that it is. Many a man who contracted the disease in ‘the riot of youth’ feels he has conquered it, but it may only be sleeping; and what can bring it back is an attack of another type of illness, for example, those with the hereditary taint of insanity may find that weakened organ – the brain – under attack from the syphilis virus.”

Maudsley thought that in some “sound” patients who received the right treatment, the disease could disappear altogether; they would revert to their “primitive sound type”, as he put it. But he feared that that might be too confident a view, and that syphilis, in fact, always remained latent.

“We have godlike reason, but man has used it to make himself more brutal than the animal”; and syphilis is the punishment for this. Which went to show, he said, that all things are “indissolubly bound together as elements in the mysterious universe”.

Like so much that touched on in/sanity, the true nature of syphilis was one of the “questions which must be left to a wiser posterity… into the intense and delicate activity of organic element the senses of man have not yet succeeded in entering”. He despaired at “the confusion and uncertainty which prevail in this department of pathology”.

Of recent historical work on syphilis, I think this is the best: The Cruel Madness of Love by Gayle Davis (2008)  https://academic.oup.com/shm/article-abstract/23/1/204/1653684