A is for Arsenic (15 page)

Mrs Boynton dies while the rest of the party are away from the 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 convict
Dr 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 taking
to ‘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 samples sent to him, and obtained far greater quantities of the poison from the vomit that had dried onto the floor. To prove the poison was the same as that found in the body, Tardieu observed the effects of the extracts from the floorboards on frog hearts, where he witnessed the same reduced heartbeat. He carefully repeated his experiments, and requested more samples of floorboards from under the bed, where no vomit could have reached – Tardieu wanted to ensure that the effect on the frog hearts was being caused by the poison, and not by varnish or paint from the floor. At the subsequent trial Pommerais's defence team attempted to discredit the scientific evidence Tardieu presented, but it was compelling; Pommerais was executed for his crimes.

By the time Agatha Christie was writing
Appointment with Death
, a chemical colour reaction had been developed to detect the presence of digitalis glycosides. Unfortunately the reaction, which produced a characteristic indigo-blue or bluish-green colour, only worked in the presence of large quantities of the drug, far greater than the amounts needed to kill. Digitalis also decomposes in the body after death, so the best way to confirm its presence was by testing vomit from the victim. If vomit was
unavailable then physiological experiments on frog hearts remained the best method for detecting small quantities of digitalis extracted from a corpse. Agatha Christie makes no mention of Mrs Boynton having vomited, and it seems unlikely that she did, as her dead body is mistaken for a sleeping one. Had Mrs Boynton been sick it is reasonable to assume that someone would have called a doctor far sooner than they did.

Today, methods of detection have improved and the means of identifying compounds within the body are standardised; we no longer rely on experiments on frogs. Analysis of the blood is the standard procedure, and even the minute quantities prescribed for daily medication are detectable. Digoxin levels of 0.6–2.6ng/ml
⁴⁸
are considered to be at a therapeutic level, and above 2ng/ml would be considered toxic, though individual responses to the drug vary greatly. The drug is released from the muscles of the heart after death, so levels may be unnaturally elevated above those expected for therapeutic doses. In the case of Mrs Boynton, it would have been possible to prove the cause of death using 1938 scientific methods; a post-mortem is ordered, but Poirot doesn't bother to wait for the results. His superior brain is capable of solving the crime before it is confirmed that a crime has even been committed.

The obvious suspects in the case are Mrs Boynton's family. Her daughter-in-law is responsible for measuring out the digitalis mixture that Mrs Boynton took daily, though the exact composition of the prescription is not mentioned. She may have been taking digitalis, a mixture of all the cardiac glycosides extracted from foxgloves, or she may have been taking a purified form of just one of them. Any one of the family could have tampered with her medicine and increased the dose by concentrating the drug, resulting in a higher than normal dose being given. Alternatively, they could have diluted the drug or substituted a placebo, causing Mrs Boynton's heart condition to worsen in its absence. Digitalis can act as a cumulative poison because it has such a long half-life in the
body, but unless the dose was significantly larger than usual Mrs Boynton would have been expected to show a gradual increase in the symptoms of digitalis intoxication, such as problems with eyesight and an irregular heartbeat, rather than a sudden collapse.

Poirot has his doubts about someone having tampered with the medication, not only because Mrs Boynton's death was very sudden, but also because of the mark of the hypodermic syringe on her wrist. He finds it implausible that a member of the family would go to the trouble of stealing a syringe and a supply of digitalis when they had far easier access to Mrs Boynton's own medication. The fact that the fatal dose was administered by hypodermic syringe suggests that another member of the party at Petra was the murderer. What Poirot does not find implausible is that someone who wanted to kill Mrs Boynton, and happened to bump into her on holiday, knew her well enough to know about her health as well as the effects of an overdose of digitalis. The murderer was also fortunate to be on a trip with a doctor who had a supply of the drug in his bag, and was prepared to risk being seen stealing the drug and the syringe from the doctor before finding an opportunity to administer the poison unobserved.

The circumstances that lead to the death of Mrs Boynton may be slightly implausible – in the stage adaptation of
Appointment with Death
Christie changed both the motive and the murderer. But her scientific descriptions throughout the book are top-notch.

Notes

⁴¹
Clinical psychologists and psychiatrists are required to have medical training. This proves to be very handy in this book.

⁴²
‘Physic' meaning ‘medicine' in this case – an obsolete usage of the word. This does, though, explain why doctors are sometimes referred to as ‘physicians'.

⁴³
Distinguishing between the different digitalis compounds, either by name or chemical structure, can feel like a game of spot-the-difference. I am still amazed how such tiny differences can result in dramatic increases in potency.

⁴⁴
An ion in this case is an atom that has lost one or more electrons.

⁴⁵
Na+/K+-ATPase is a bit of a mouthful; it's an enzyme that controls the movement of sodium (Na
+
) and potassium (K
+
) ions across cell membranes. This movement causes an electrical impulse in nerves, and also triggers the movement of other ions such as calcium (Ca
2+
) in muscles to cause contractions.

⁴⁶
These are 500–700 nanometres (nm) (red), 450–630nm (green), and 400–500nm (blue).

⁴⁷
Known as cGMP – short for cyclic guanosine monophosphate.

⁴⁸
ng = nanogram. A tiny amount, in other words.

Crooked House

If Brenda were to make a mistake and inject eyedrops into me one day instead of insulin – I suspect I should give a big gasp, and go rather blue in the face and then die, because you see, my heart isn't very strong.

Agatha Christie,
Crooked House

IN the quote above, Aristide Leonides is describing the details of his own death. He dies when he is injected with eserine eyedrops, which had been substituted for his regular dose of insulin. Eserine is an unusual choice of poison; Agatha Christie used it in only two of her novels,
Crooked House
and
Curtain
. You might expect a poisoner to have a detailed medical or pharmaceutical knowledge in order to choose eserine, but in
Crooked House
, Christie ensures there are plenty of suspects by giving Aristide a big audience when he speaks these prophetic words. Aristide is actually answering a question from his
granddaughter as she looks at his bottles of medicine – ‘Why does it say “Eyedrops – not to be taken” on the bottle?' His extended family seated around him all hear his reply; one of them goes on to use the old man's own medicine to kill him.

The list of suspects in
Crooked House
is a long one: there is Aristide's second wife Brenda; his
first
wife's sister, Edith; his sons, Philip and Roger; his sons' wives, Magda and Clemency; and his three grandchildren, Josephine, Eustace and Sophia. There is also the household staff, including the cook, the tutor and the nanny; they all live together with the ‘crooked man' Aristide in his ‘crooked house'. But this time there is no Hercule Poirot or Miss Marple on hand to help identify the culprit. Instead it is down to the detective powers of the police and Sophia's fiancé, Charles Hayward, to do their best. In the novel, Christie scrupulously presents every clue to her readers, and even hints strongly at the murderer. However, when the culprit is finally revealed it still comes as a shocking revelation (Christie's publishers even had the nerve to ask her to change it, but she refused).

The poison used, eserine, had come a long way to arrive in the Leonides household. This compound is an extract from the beans of a West African plant,
Physostigma venenosum
. Eserine has had a variety of applications in medicine, from the management of glaucoma to emergency treatment for nerve-gas poisoning. There have been cases of accidental eserine poisoning, but criminal poisonings are exceptionally rare, perhaps owing to a combination of eserine's low profile and because treatment is readily available and very effective; eserine victims have a good chance of survival.