A is for Arsenic (37 page)

The question of chronic strychnine poisoning is raised at the inquest. Could the levels of strychnine have built up in Mrs Inglethorp's body over several days, resulting in a final, fatal dose? Chronic strychnine poisoning is unlikely; the compound is eliminated from the body fairly rapidly, either unchanged or modified by enzymes in the liver, with a half-life of about ten hours. However, anyone with liver disease such as hepatitis or chronic alcoholism would be more susceptible because their liver would not be working efficiently, and the drug might accumulate in the organ. Mrs Inglethorp was in good health, but anyone suffering from the combined effects of liver disease and chronic strychnine poisoning would be likely to display symptoms such as twitching or tremors. If an error had been made when the tonic was made up and this had resulted in a stronger solution, it would have produced clear symptoms in the victim rather than one sudden, dramatic and fatal attack.

It was not one drug that did away with Mrs Inglethorp; it was a combination of three compounds and a lot of planning. Of all the possible sources of strychnine to be found in the house, it was Mrs Inglethorp's own tonic that caused her death. The whole bottle of tonic contained enough strychnine to kill, but it all had to be concentrated into the final dose. This was actually simple to achieve.

Strychnine is poorly soluble in water and is normally converted into a salt form to increase its solubility, but the choice of salt is important as not all strychnine salts dissolve well in water. Strychnine sulfate was used to make up the tonic, and this would dissolve perfectly well to leave a clear, colourless solution with the strychnine distributed evenly throughout the bottle. A problem occurs if other salts are added to the mix. Depending on the salt used, it can cause the strychnine salt to convert from a soluble to an insoluble form. Potassium bromide added to a solution of strychnine sulfate would cause, over the course of a few hours, the formation of
colourless crystals of strychnine bromide, which would settle to the bottom of the bottle.

The potassium bromide needed to precipitate the strychnine was obtained from Mrs Inglethorp's bromide powders. One or two powders would have been added to the tonic when it was purchased. This would have been more than enough to create the desired crystallisation of strychnine bromide. The addition of the powders to the tonic would not have changed its appearance or taste. Potassium bromide dissolves in water easily to form a colourless solution and has only a slightly sweet taste when dilute but a bitter taste at higher concentration. If the person who administered the tonic did not shake the bottle before pouring out Mrs Inglethorp's regular dose, the victim would have swallowed almost the entire quantity of strychnine in one go. Addition of morphine, or another narcotic, to the cocoa would delay the onset of strychnine poisoning and divert attention from the tonic, which Mrs Inglethorp took just before going to bed.

To explain this highly devious method to Captain Hastings, Poirot reads from a book on dispensing he found at the hospital dispensary.

The following prescription has become famous in text books:

Strychnininae Sulph …………… gr. I

Potass Bromide ………………….. 3vi

Aqua ad ……………………………… 3viii

Fiat Mistura
⁹⁵

This solution deposits in a few hours the greater part of the strychnine salt as an insoluble bromide in transparent crystals. A lady in England lost her life by taking a similar mixture: the precipitated strychnine collected at the bottom and in taking the last dose she swallowed nearly all of it!

The above text is taken from
The Art of Dispensing
, which Christie would have studied for her exams when she qualified as a dispenser.

The descriptions by Agatha Christie of strychnine and its poisonous effects are very accurate in all the stories where she uses it. The chemical knowledge needed to plot a murder mystery such as
The Mysterious Affair at Styles
is considerable, and as I mentioned earlier, this was remarked upon at the time in a review of the novel in the
Pharmaceutical Journal and Pharmacist
. The academic journal praised her scientific accuracy in the novel; no wonder she was so proud of this review.

Notes

⁹⁰
Another poison, brucine, is found in the bark of the shrub.

⁹¹
Steps can also be taken to prevent convulsions by keeping the patient calm and still in a dark and quiet room. Without stimuli, the nerves will not send signals, allowing time for the strychnine to be eliminated from the body.

⁹²
Yes, we have seen almost exactly the same story before – a different Frenchman, on a different date, with a different poison, arsenic (see page
here
). The French Academy of Medicine clearly needed some persuading as to the merits of activated charcoal.

⁹³
You can probably see where this is going.

⁹⁴
The noose is supposed to have choked off the end of the sentence. But sadly this is not the solution to the Jack the Ripper case, as Cream was in prison at the time that one of the murders took place. It could represent a bit of showmanship on his part – he seemed to crave notoriety. More likely, the story was made up after the event, as there was no mention of it at the time. Perhaps the hangman invented the story, to claim the credit for hanging this infamous murderer.

⁹⁵
‘Fiat mistura' roughly translates as ‘becomes a mixture'.

The Pale Horse

I looked and there before me was a pale horse! Its rider was named Death, and Hell was following close behind him.

Revelations
6:8

THE ‘Pale Horse' of Agatha Christie's novel was an organisation that arranged deaths on demand. At the Pale Horse Inn, a witches' coven of contract killers appears to commit murder for money. None of the so-called witches meets any of the victims, all of whom seem to die of natural causes. Paranormal theories abound, but there is a much more down-to-earth explanation. Mark Easterbrook, an historian and writer, is drawn into the mystery when he witnesses a fight between two girls in a coffee shop, one of whom has a clump of hair pulled from her head. A week later he sees that one of the girls from the fight has died, and this is just one from a list of unexpected deaths. A series of unusual events
leads Easterbrook to suspect foul play, and he sets out to prove that the deaths are connected and that someone, somewhere, is responsible for them. It turns out that thallium has been given to all of the victims in low, regular doses, which accumulate in the body and finally kill after days, or even weeks, of pain and suffering.

Thallium is sometimes known as the ‘poisoner's poison'. It was little known prior to the publication of
The Pale Horse
in 1961, and so was rarely tested for in post-mortems. The idea of using this element in a murder plot was suggested to Christie by an American doctor, but she must have carried out considerable independent research to develop her detailed knowledge of this rarely used poison. Thallium poisoning can result in a wide range of symptoms that are easily attributed to many different natural diseases. Despite the obvious benefits of thallium to the murder-mystery writer, Agatha Christie uses it in just one novel. What she lacks in the number of books, though, she more than makes up for in the number of deaths. A total of ten victims are named in
The Pale Horse
, with more murders implied.

This book has gained some notoriety, and it has even been suggested that it was the inspiration for several real-life murders. But from another point of view, Christie's writing about the symptoms of thallium poisoning in such a prominent and accurate way raised awareness of this deadly element, and may even have saved lives.

The
Thallium story

Thallium (Tl) is the 81st element in the periodic table; in its pure state it is a soft grey metal. It was indirectly (and independently) discovered in 1861 by William Crookes (1832–1919) and Claude-Auguste Lamy (1820–1878). They had been analysing different materials by burning them and observing the colour of the flame produced, using a recently invented technique called flame spectroscopy. This method splits light up into its component colours. Each element in the periodic table burns with a characteristic colour, so different elements present
in a sample can be identified using a spectrometer. Flame spectroscopy is still in use today; a version of this technique known as atomic absorption spectroscopy can be used to analyse tissue and fluids from a body at a post-mortem to identify poisonous elements such as arsenic, mercury and thallium.

In the samples analysed by Crookes and Lamy, a flame colour was observed in the ‘green' part of the spectrum, where no element had previously been observed, so they knew there must have been an unknown element present. The green colour led Crookes to name it ‘thallium', after the Greek
thalos,
meaning ‘green shoot or twig'. Crookes continued his experiments on the new element, and announced his discovery in the March 1861 issue of
Chemical News
. Lamy announced
his
discovery some months later, and an almighty row ensued over who had prior claim to the discovery. To keep the peace, credit was given to both scientists. However, what both Crookes and Lamy had actually discovered was a
compound
of thallium, and not the pure element. The world had to wait another year for Lamy to isolate the element and produce a tiny ingot of pure thallium.

Thallium is relatively abundant on Earth but is only thinly distributed in rocks and soils, because it reacts readily to form compounds that are often very soluble. Water will erode away thallium salts and deposit them elsewhere in an endless process of redistribution. This means that thallium, despite its toxicity, is not considered to be an environmental pollutant as people, livestock and crops are highly unlikely to be exposed to dangerous levels. Unlike thallium salts, which have no odour, very little taste and are highly toxic, thallium metal is unlikely to poison anyone, because it is not soluble in water and therefore cannot be transported into the body easily.
⁹⁶

Besides their potential as poisons, thallium salts have several applications, though their use is carefully monitored and controlled today. Thallium oxide and some other thallium compounds are added to specialist glass to increase the refractive index (the degree to which light bends when it passes through a different material). These specialist glasses are used in the optics industry, to make camera lenses, for example. Once in the glass the thallium compound is trapped, and completely safe as it cannot leach out. Other modern applications include uses in components in the electronics industry.

Before their toxicity was properly realised, thallium salts had applications in medicine. One effect of administering thallium salts was discovered by accident in the 1890s, when thallium acetate (TlCH
3
CO
2
) was given to tuberculosis patients in the hope that it would reduce the night sweats they experienced. It had no effect on these at all, but the patients' hair fell out. Hair loss today would be considered a symptom of damage to the body, but at the time this was seen as a potential benefit, particularly for the treatment of ringworm.