‘So I learned, sir, so I learned. But not so well known to the public. The medical profession is at pains not to reveal too much about it, since it only arises in connection with inoculation experiments. I have it on authority that a number of human patients are reported to have died in that way after experiments in Germany. It’s liable to hold up mass-inoculation by several years until it’s properly understood. But even if the doctors can’t explain why it happens, they understand the conditions that are conducive to it.’
‘The vaccines used in the German experiments were prepared with chick embryos, and the patients who died were sensitive to eggs. I don’t know where this is leading us, Sergeant.’
‘Don’t you, sir? Well, as I understand it, the kind of violent reaction the doctors call acute respiratory shock can be induced in the laboratory. It was done as early as 1839 by the famous French physiologist, Francois Magendie, injecting dogs with egg-white. He discovered that two injections of egg-white at an interval of fourteen days produced acute respiratory shock. After the second injection the dogs died within five minutes. Now the curious thing is that egg-white isn’t what you’d call a death-dealing substance. In fact, it’s usually regarded as an antidote. It was obviously something to do with the period between the injections, because dogs injected after one week suffered no effect at all. More recently, a series of experiments on guinea-pigs produced the same dramatic result when they received a second injection of dog-serum.’
‘You have been busy, Sergeant.’
‘So the German doctors now believe that the acute respiratory shock in their patients was a similar reaction. The patients who died reacted to the vaccine, as you suggest, but some two weeks before receiving the injection they had become sensitised-is that the word? — to eggs, perhaps by eating them in some form, possibly even in a cake. When they were injected with the vaccine a fortnight later, the effect was as sudden and violent as if they had been given strychnine-except, of course, that the post mortem examination showed only the kinds of symptoms associated with death from chronic asthma.’
‘Oh, it’s eggs, is it?’ said Prothero. ‘I murdered my son with a boiled egg, did I-or was it a Madeira cake?’
‘If you’ll kindly allow me to go on,’ said Cribb, ‘you’ll see that I’m suggesting no such thing. People can be sensitive to other things besides eggs. You’ll allow that asthma results from reactions to certain substances and emanations?’
‘I can hardly deny it, having written a paper on the subject. Hay, pollen, ipecacuanha, bedfeathers, house-dust. A patient may be affected by any one of these, or something else. My son was sensitive to pollen.’
‘Really, sir?’ said Cribb. ‘Now suppose an asthma patient were discovered to be vulnerable to one of the substances you mention, rather as those Germans were sensitive to egg-white, and someone injected them with a small amount of the substance. What would the result be, do you think?’
‘Quite neutral, I should think. The substances affect the breathing, not the blood.’
‘Ah, but what if a second injection were given two weeks later?’
‘That would be a dangerous thing to try, Sergeant. It might well result in the phenomenon you have described.’ Prothero leaned forward across the table, ‘But if that was how it happened, you would have found a recent injection-mark on my son’s body. There was none-in spite of the inordinately careful examination made by the doctors at the post mortem.’
‘That’s where my theory foundered,’ said Cribb, ‘until I took professional advice. I put the case to my Harley Street specialist-hypothetically, of course, with no names mentioned. If a man with the specialised knowledge of substances that cause asthma and similar conditions were to take it into his head to kill another human being, I said, and chose a victim with a known sensitivity to, say, pollen, and a history of asthma, how would he induce the phenomenon known as acute respiratory shock? By grinding the pollen to a fine powder, said my adviser and then taking a very small amount, as little as a tenth of a milligram, and injecting it into the victim, perhaps secreted in some other substance administered in the course of treatment. Then if two weeks later he were suddenly exposed to a slightly larger quantity of the substance, say a milligram, he would die within five minutes. The amounts involved would be so small as to be impossible to detect in a post mortem. Did the second quantity of the substance have to be introduced by means of an injection, I asked? No, said he, certain substances are readily absorbed by skin tissue-nettle leaf irritant, for example, or pollen.’
‘This is all very plausible,’ said Prothero, ‘but when Guy died we were not in a bed of nettles, Sergeant, nor were we coating ourselves with pollen in the hotel garden. So far as I can recollect, there were not even any flowers in the lounge.’
‘I established that, sir. Went over everything I could think of until I was ready to give up. Then, as sometimes happens, I was thinking of something quite unconnected with the case, when the very thing I needed to know flashed across my mind. It was the statement the inspector made after I arrived and found you both there with Guy’s body. He told me the answer, and I was too damned unreceptive to accept it. What were his words, sir? — “it seemed at first to be the consequence of an over-enthusiastic inhalation of snuff.” That’s how you did it, Dr. Prothero. The pollen was in the boy’s snuff-box. One inhalation was enough to kill him. You’d mixed it with the snuff that morning knowing Guy wouldn’t take any on the ride, but would probably inhale it after lunch.’
‘You’ve had the contents of the snuff-box analysed, I have no doubt,’ said Prothero.
‘I have, sir, and as you very well know there ain’t a microscope invented with sufficient power to detect a quantity of pollen as small as that, nor a chemical test to prove its presence. It’s as neat a way of ending a fellow-human’s life as I’ve ever come across. A doctor’s way.’
‘A father’s,’ said Prothero, after a pause, ‘and not neat, Sergeant.’
‘The boy would have killed again if he had lived,’ said Cribb. In their context the words were reassuring. For the first time all pretence between the two men had been abandoned. They observed each other with candour, if not respect.
‘There is a saying of Hippocrates, the founder of our profession,’ said Prothero, ‘“Extreme remedies are most appropriate for extreme diseases”. Believe me when I tell you that I did all I could for Guy while he was alive. At the last, I had to ask myself what future there was for him. I know of other cases, Sergeant, poor wretches with the same dreadful impulse for violence who are kept behind locked doors by devoted parents. Can you imagine what will happen when one of them one day finds a way to slip the latch-for they are intelligent beings as Guy was? The mayhem and the carnage will be beyond belief, Sergeant, striking terror into people’s hearts long after the poor demented creature is recaptured by the police or his wretched family. Am I exaggerating?’
‘I hope so, sir,’ said Cribb quietly. ‘I think we’d better move in the direction of the station.’
Prothero raised his eyebrows questioningly. ‘Railway-or police?’
‘I’d never be able to prove my case in court,’ said Cribb with a slight smile. ‘Damned lawyers aren’t going to get a conviction out of nothing more substantial than an extra week in Brighton. . Unless you’ve decided to make a confession. But, as I said, I didn’t bring a man with me, or the handcuffs, and it’s devilish hard to hear anything anyone says on those confounded trains. I think we’ve just time to catch that 4.23.’
Albert Moscrop finished polishing the latest example of his handiwork, a small, brass telescope with a magnification of four diameters. It represented some three weeks’ work, mainly in the evenings, after the shop was closed. He had begun on the day when he had read the newspaper report of the inquest on Bridget. She had been murdered, it had said, by a person or persons unknown, but it was understood that the police had indicated that there was nothing to be gained from further inquiries into the case.