“I do not know whether you quite followed all the technical arguments about this. I will try to tell you the chief points as I understood them. The nature of arsenic is to pass through the body very quickly, especially if it is taken with food or immediately following a meal, because the arsenic irritates the lining of the internal organs and speeds up the process of elimination. The action would be quicker if the arsenic were taken in liquid than if it were taken in the form of a powder. Where arsenic was taken with, or immediately on top of, a meal, nearly the whole of it would be evacuated within twenty-four hours after the onset of the illness. So you see that, although the actual quantities found in the body may seem to you and me very small indeed, the mere fact that they were found there at all, after three days of persistent vomiting and diarrhoea and so on, points to a large dose having been taken at some time.

“Now there was a great deal of discussion about the time at which the symptoms first set in. It is suggested by the defence that Philip Boyes may have taken arsenic himself at some time between leaving Harriet Vane’s flat and hailing the taxi in Guilford Street; and they bring forward books which show that in many cases the onset of symptoms takes place in a very short time after taking the arsenic – a quarter of an hour, I think, was the shortest time mentioned where the arsenic was taken in liquid form. Now the prisoner’s statement – and we have no other – is that Philip Boyes left her at 10 o’clock, and at ten minutes past he was in Guilford Street. He was then looking ill. It would not take many minutes to drive to Woburn Square at that hour of night, and by the time he got there, he was already in acute pain and hardly able to stand. Now Guilford Street is a very short way from Doughty Street – perhaps three minutes’ walk – and you must ask yourselves, if the prisoner’s statement is correct, what he did with those ten minutes. Did he occupy himself in going to some quiet spot and taking a dose of arsenic, which he must in that case have brought with him in anticipation of an unfavourable interview with the prisoner? And I may remind you here, that the defence have brought no evidence to show that Philip Boyes ever bought any arsenic, or had access to any arsenic. That is not to say he could not have obtained it – the purchases made by Harriet Vane show that the law about the sale of poisons is not always as effective one would like it to be – but the fact mains that the defence have not been able show that the deceased ever had arsenic in his possession. And while we are on the subject, I will mention that, curiously enough, the analysts could find no traces of the charcoal, or indigo, with which commercial arsenic is supposed to be mixed. Whether it was bought by the prisoner or by the deceased himself, you would expect to find traces of the colouring matter. But you may think it likely that all such traces would be removed from the body by the vomiting and purging which took place.

“As regards the suggestion of suicide, you will have to ask yourselves about those ten minutes – whether Boyes was taking a dose of arsenic, or whether, as is possible, he felt unwell and sat down somewhere to recover himself, or whether, perhaps, he was merely roaming about in the vague way we sometimes do when we are feeling upset and unhappy. Or you may think that the prisoner was mistaken, or not speaking the truth, about the time he left the flat.

“You have also the prisoner’s statement that Boyes mentioned, before he left her, that he was feeling unwell. If you think this had anything to do with the arsenic, it of course disposes of the suggestion that he took poison after leaving the flat.

“Then, when one looks into it, one finds that this question about the onset of symptoms is left very vague. Various doctors came here and told you about their own experiences and the cases quoted by medical authorities in books, and you will have noticed that there is no certainty at all about the time when the symptoms may be expected to appear. Sometimes it is a quarter of an hour or half an hour, sometimes two hours, sometimes as much as five or six, and, I believe, in one case as much as seven hours after taking the poison.”

Here the Attorney-General rose respectfully and said: “In that case, me lud, I think I am right in saying that the poison was taken on an empty stomach.”

“Thank you, I am much obliged to you for the reminder. That was a case in which poison was taken on an empty stomach. I only mention these cases to show that we are dealing with a very uncertain phenomenon, and that is why I was particular to remind you of all the occasions on which Philip Boyes took food during the day – the 20th of June – since there is always the possibility that you may have to take them into consideration.”

“A beast, but a just beast,” murmured Peter Wimsey.

“I have purposely left out of consideration until now another point which arose out of the analysis, and that is the presence of arsenic in the hair. The deceased had curly hair, which he wore long; the front portion, when straightened out, measured about six or seven inches in places. Now, in this hair, arsenic was found, at the end closest to the head. It did not extend to the tips of the longest hair, but it was found near the roots, and Sir James Lubbock says that the quantity was greater than could be accounted for in any natural way. Occasionally, quite normal people are found to have minute traces of arsenic in hair and skin and so on, but not to the amount found here. That is Sir James’ opinion.

“Now you have been told – and the medical witnesses all agree in this – that if a person takes arsenic, a certain proportion of it will be deposited in the skin, nails and hair. It will be deposited in the root of the hair, and as the hair grows, the arsenic will be carried along with the growth of the hair, so that you get a rough idea, from seeing the position of the arsenic in the hair, how long the administration of arsenic has been going on. There was a good deal of discussion about this, but I think there was fairly general agreement that if you took a dose of arsenic, you might expect to find traces of it in the hair, close to the scalp, after about ten weeks. Hair grows at the rate of about six inches a year, and the arsenic will grow out with it till it reaches the far end and is cut off. I am sure that the ladies on the jury will understand this very we11, because I believe that the same thing occurs in the case of what is termed a ‘permanent wave.’ The wave is made in a certain portion of the hair, and after a time it grows out, and the hair near the scalp comes up straight and has to be waved again. You can tell by the position of the wave, how long ago the waving was done. In the same way, if a finger-nail is bruised, the discolouration will gradually grow up the nail until it reaches the point where you can cut it off with the scissors.

“Now it has been said that the presence of arsenic in and about the roots of Philip Boyles’ hair indicates that he must have taken arsenic three months at least before his death. You will consider what importance is to be attached to this in view of the prisoner’s purchases of arsenic in April and May, and of the deceased’s attacks of sickness in March, April and May. The quarrel with the prisoner took place in February; he was ill in March and he died in June. There are five months between the quarrel and the death, and four months between the first illness and the death, and you may think that there is some significance in these dates.

“We now come to the enquiries made by the police. When suspicion was aroused, detectives investigated Harriet Vane’s movements and subsequently went to her flat to take a statement from her. When they told her that Boyes was found to have died of arsenic poisoning, she appeared very much surprised, and said,‘Arsenic? What an extraordinary thing!’ And then, she laughed, and said, ‘Why, I am writing a book all about arsenic poisoning.’ They asked her about the purchases of arsenic and other poisons which she had made and she admitted them quite readily and at once gave the same explanation that she gave here in court. They asked what she had done with the poisons, and she replied that she had burnt them because they were dangerous things to have about. The flat was searched, but no poisons of any kind were found, except such things as aspirin and a few ordinary medicines of that kind. She absolutely denied having administered arsenic or any kind of poison to Philip Boyes. She was asked whether the arsenic could possibly have got into the coffee by accident, and replied that that was quite impossible, as she had destroyed all the poisons before the end of May.”