Free A is for Arsenic by Kathryn Harkup Page B

camp, so there are no witnesses to her final moments. Doubts about a natural cause of death are raised when Dr Gerard notices a mark on Mrs Boynton’s wrist, the sort of mark that would be left by a hypodermic syringe. He also notices that the bottle of digitoxin in his medicine bag has been noticeably depleted, even though he hasn’t used any during his trip, and his hypodermic syringe is missing. To clarify the cause of death requires a post-mortem examination of the body as a first step, but conducting a post-mortem in an ancient abandoned city is not practical, so Mrs Boynton’s body is taken to Amman … which happens to be the city in which Hercule Poirot is on vacation.
    As Agatha Christie correctly points out, ‘the active principles of digitalis may destroy life and leave no appreciative sign’. Even so, a large dose would be detectable if the pathologist knew to look for it. The presence of digitalis was first detected in a murder victim in 1863; scientific evidence helped convictDr Edmond-Désiré Couty de la Pommerais of the murder of his former mistress, Madame Séraphine de Pauw. Pommerais had convinced Pauw to take part in an elaborate insurance swindle in order to pay off his debts. A number of large insurance policies were then taken out on Pauw’s life. Pommerais told her that his plan was to convince the insurance companies that Pauw had a terminal illness and would die soon, at which point they would claim a large annuity until she died rather than pay out the vast sums of insurance money. She would then miraculously recover to live the rest of her natural life in financial security. Séraphine even told her sister of the ingenious plan; but the sister saw through Pommerais’s promises, and warned Séraphine that he might be planning to kill her and keep all the money for himself.
    This is exactly what happened. On 16 November 1863, Pommerais gave Pauw something that made her very ill but, as was predicted by her sister, Madame Séraphine did not recover. Pommerais filed his claims with the insurance company and sat back, presumably reassured that the poison he had chosen to kill his victim could not be traced. The police, however, were suspicious of Pommerais’s behaviour; they asked Ambroise Tardieu (1818–1879), a respected medical doctor, to analyse Pauw’s body for signs of poisons. After eliminating metals such as arsenic and lead, Tardieu turned to the alkaloids. Using the Stas method (see page here ), Tardieu managed to extract a bitter-tasting substance from Pauw’s remains. However, Tardieu could not identify the substance; it was not an alkaloid with which he was familiar. After a series of fruitless experiments, and almost at his wits’ end, Tardieu decided to inject five grains of the extract (approximately 300mg) into ‘a large vigorous dog’ to see what would happen. The answer was – absolutely nothing, for two and a half hours. Then the dog suddenly vomited and lay down, obviously weak. The dog’s heart slowed, beat irregularly and occasionally stopped until twelve hours later, when the beast began to recover. Looking at correspondence between Séraphine and Pommerais, Tardieu found discussions of a prescription of digitalis she was takingto ‘stimulate herself’. This had all been part of the ruse to obtain money from the insurance companies, but it gave Tardieu the clue he needed – the victim had died from digitalis poisoning.
    Tardieu had not recovered enough digitalis from Pauw to account for her death. He explained to the police inspector that what he really needed was a sample of her vomit; this would contain a much higher concentration of the poison, enough perhaps for him to establish a cause of death. The inspector responded to this in a remarkable way. No samples of vomit had been retained, so he went back to Pauw’s bedroom, and removed floorboards and wood shavings from parts of the floor where vomit had been spilled. Tardieu quickly set about analysing the