A is for Arsenic (32 page)

Even without the possibly dubious results of a post-mortem, Poirot finds other evidence that phosphorus has been given to Miss Arundell. A few days before her death, and the night Miss Arundell started to feel unwell, she took part in a seance. During the seance a ribbon of glowing vapour was seen to issue from Miss Arundell's mouth, forming a halo around her head. The halo was witnessed by several people but attributed to ectoplasm, or some spectral manifestation. Only Poirot realises it was the green glow of phosphorus vapour.

Poirot describes how the halo of light was some ‘phosphorescent' substance; he misuses this term, which technically refers to the glow emitted by a substance that has been charged by light shining on it, and continues to glow in the dark (exit signs in cinemas, for example), although the word does have its origins in the glow observed when phosphorus is exposed to the air. Phosphorus actually
chemiluminesces
; light is produced as the result of a chemical reaction (other examples of this include the bottoms of female fireflies, or the glow-sticks waved by night-clubbing ravers). The exact cause of the glow emanating from white phosphorus was not fully explained until 1974, so Poirot can hardly be blamed for his mistake back in 1937. A chemical reaction between phosphorus atoms and oxygen atoms produces diphosphorus dioxide (P
2
O
2
) and monophosphine oxide (HPO) molecules that only exist
fleetingly, but both of which emit light. A piece of white phosphorus will glow in a stoppered flask until either all of the oxygen or all of the phosphorus has been consumed in the reaction. Looking back at the spectral halo, body temperature would have increased the amount of vapour produced from the phosphorus in the stomach, and as Miss Arundell breathed out, the vapour may have been visible as it reacted with the oxygen in the air and began to glow.

Confusing the glow of phosphorus for ectoplasm at a seance is not as far-fetched an idea as it may sound. Many people have tried to explain unusual phenomena such as graveyard ghosts, will-o'-the-wisps and spontaneous human combustion as phenomena caused by phosphorus, either from the glow of elemental phosphorus reacting with oxygen, or through a phosphorus-based compound spontaneously catching fire in the air. It has long been known that in marshes, bogs and other areas where organic matter decays, methane (CH
4
) is produced by bacteria in the anaerobic (oxygen-free) conditions found in the damp soil. Methane burns very effectively but it needs a source of ignition, which could be from phosphine (PH
3
) or diphosphane (P
2
H
4
); these compounds can also be produced by anaerobic bacteria, and they spontaneously combust when exposed to air. The theory goes that phosphine or diphosphane is slowly emitted from the soil, catches fire and triggers the burning of methane to produce the elusive flickering flames known as will-o'-the-wisp, or
ignis fatuus
(foolish fire). Similarly, the reaction of phosphorus with stomach acid could produce phosphine gas, which could react spontaneously with the air when breathed out.

Even if the real reason for Miss Arundell's final illness had been determined before she died, very little could have been done. In the early stages of phosphorus poisoning it is hoped that the vomiting will remove most of the poison from the system, and water can be given to the victim between bouts. Once Poirot is convinced that Miss Arundell died of phosphorus poisoning, he sets about proving how it was done. Miss Arundell's symptoms began in the late evening, indicating
that she had been poisoned around dinner time. Poirot questions the nurse who attended Miss Arundell in her last illness to find out who prepared her food, and who had access to the sick room. It was found that the prime suspect, a faithful companion, never went near the food and was rarely in the sick room. Only the servants and the nurse would have been in a position to administer poison in the food, and they were all above suspicion.

Miss Arundell was in the habit of taking two or three pills after each meal. Could these have been the source of poison? We were not told what medicine Miss Arundell's doctor prescribed to her, but we are assured it was mild. We also learn that Miss Arundell was taking a patent medicine, Dr Loughbarrow's Liver Pills, which contained aloes (used as a herbal medicine, usually a laxative) and podophyllin (once used as a resin to treat genital warts). Despite the doctor's assurances, podophyllin is quite a toxic substance, and overdoses can lead to depression and even death. It is used mostly in patent medicines to treat constipation or to increase secretion of bile, but it is not recommended for anyone suffering from jaundice. Christie seems unaware of the complications of podophyllin, and considers these pills to be innocuous.

Phosphorus has been used as a medical treatment in the past; its popularity waxed and waned over a period of 300 years before it was finally abandoned. The source of phosphorus and its glow were seen as evidence of the vital ‘flame of life', as Robert Boyle put it – the
flammula vitae
. Phosphorus pills, carefully coated to prevent them from reacting with the air, were prescribed in the early eighteenth century for colic, asthmatic fevers, tetanus, apoplexy and gout. None of these treatments would have worked, and the larger doses of phosphorus would kill. The dangers were soon realised, a mere 90 or so years later, and phosphorus started to disappear from the regular pharmacopoeia. However, it was still used, in
ever-lower doses, for the treatment of conditions as varied as tuberculosis and epilepsy. In the early twentieth century phosphorus was still being prescribed as a general tonic, but by 1932 it had disappeared from the
British Pharmacopoeia,
though it persisted in some remedies until the 1950s. When
Dumb Witness
was written in 1937, phosphorus would not have been prescribed and, even if it was found in over-the-counter remedies, the dose would be in the region of 0.5–3mg, well below the lethal dose. These pills would gradually become safer the longer they were left on the shelf or in the medicine cabinet, as more and more of the white phosphorus was oxidised into safer compounds over time.

Dr Loughbarrow's Liver Pills are an invention of Agatha Christie, but very similar pills were sold for neuralgia or as a general tonic. In 1931 a Dr G. Coltart wrote in the
Lancet
about a case he had prescribed for in 1904. A patient had come to him complaining he felt ‘run down', so a prescription for a common tonic pill, which contained strychnine and phosphorus, was made out for him. The patient was told to stop taking the pills if the strychnine made him twitch. Twenty-seven years later, the patient returned with a severe case of phossy jaw. Asked why he had continued to take the pills he said they had never made him twitch.

There was no phosphorus in Miss Arundell's medicine, but the medicine could have been tampered with. The liver pills were in the form of gelatin capsules, two halves fitted together to enclose the powdered medicine inside. All the murderer had to do was get one of the capsules, empty it of its normal herbal remedy and add powdered white phosphorus in its place. A lethal dose of 100mg of phosphorus would easily fit inside such a capsule, and more could be added just to make sure. A single adulterated pill added to a box of 50 pills could be taken at any time, and the murderer was unlikely to be present.

As Poirot points out, phosphorus was easy to obtain from rat paste. Rodine rat poison was sold in pharmacies across the UK, and a one-ounce tin contained ten grains of phosphorus
(approximately 650mg), enough to kill six people. Poirot also suggests that a trip abroad might provide an even easier source of phosphorus, as white phosphorus-based matches continued to be sold in many places long after they had been banned in Britain. Poirot, of course, pieces together all the circumstantial evidence, exposing the murderer and allowing justice to take its course.

Notes

⁷⁸
Entitled
Poirot Loses a Client
in the United States.

⁷⁹
c
.1630 to either
c
.1692 or
c
.1710. The dates are hazy.

⁸⁰
The mythical philosopher's stone (much popularised in recent times by a certain boy wizard) was believed to be the key to turning base metals into gold. It's what every alchemist was searching for, along with the elixir of life and the universal solvent (the last of which is particularly bewildering; if you found it, what would you keep it in?).

⁸¹
I worked with phosphorus-based compounds for many years; their smell is very powerful and uniquely unpleasant. The smell is often described as ‘garlicky', but in reality it is like nothing else on Earth.

⁸²
Matilda was an Austrian princess, betrothed to the future King of Italy, Umberto I. She trod on a match as she leaned out of a window to talk to a relative; her dress was on fire before she realised what had happened. Matilda subsequently died of her injuries.

⁸³
Eating match-heads was a popular suicide method for a while. There was enough white phosphorus in the match-heads of one box of matches to be lethal. Today, due to the use of non-toxic red phosphorus, licking the side of a matchbox, or even several matchboxes, won't prove fatal.

⁸⁴
A quote from the pathologist.

Partners in Crime

Don't Torture Your Child!

TO MOTHERS! See your little one's terror at the very thought of a dose of castor oil, mineral oil, calomel or pills. Urgh!

Advert for ‘Cascarets Candy Cathartic', 1918

MANY people will have first-hand knowledge of the unpleasant nature of castor oil, but fortunately very few will experience the deadly effects of another extract from the same plant – ricin. This poisonous protein has considerable notoriety today, but when Agatha Christie was writing it had never been used in a murder. The lack of real-life examples may underlie some of the inaccuracies in Christie's use of the poison, a rare occurrence for the Queen of Crime. Before 1978 ricin was untreatable and untraceable, seemingly the perfect poison. In many respects Christie was years ahead of her time when she used it to poison four members of the same
household in
The House of Lurking Death
, a short story featuring two detectives, Tommy and Tuppence Beresford, which along with a number of other tales featuring the duo appears in Christie's 1929 book
Partners in Crime
.

The House of Lurking Death
begins with Lois Hargreaves asking Tommy and Tuppence to look into an attempt on her life made via some poisoned chocolates. The arsenic-laced chocolates had been sent anonymously, but Lois could prove that they must have been sent by someone in her household. Tommy and Tuppence promise to travel to Miss Hargreaves's house, Thurnley Grange, the next day to investigate. But before the pair can set off, another poisoning attempt is made. A plate of ricin-laced fig sandwiches is served for afternoon tea; this time the murderer is successful.

The ricin story

Ricin is produced by the castor oil plant,
Ricinus communis,
which occurs throughout tropical regions of the world and is often grown as an ornamental shrub. Small amounts of ricin can be found in all parts of the plant, but it is mainly concentrated in the seeds; specifically, it occurs in the endosperm, a store of oil that serves as a source of nutrition for the fertilised seed. Ricin is important for the plant, as it deters herbivorous animals from eating it (although birds such as hens and ducks appear immune to the castor oil seed's poisons). Between five and twenty raw castor oil seeds may prove fatal for an adult human if they are well chewed, but cooking the seeds inactivates the poison; anything that changes the shape of a protein is said to ‘denature' it. This can be done by heat or chemical reaction, and it is irreversible – think of the result when cooking eggs, which are primarily made up of proteins.