The Final Proof
“We now,” Thorndyke resumed, “enter the final stage of the inquiry.
Hitherto we have dealt with purely scientific evidence which would
have had to be communicated to the jury and which they would have had
to take on trust with no convincing help from their own eyes. We had
evidence, conclusive to ourselves, that Monkhouse had been murdered by
means of a poisoned candle. But we could not produce the candle or any
part of it. We had nothing visible or tangible to show to the jury to
give them the feeling of confidence and firm conviction which they
rightly demand when they have to decide an issue involving the life or
death of the accused. It was this something that could be seen and
handled that I sought, and sought in vain until that momentous evening
when I called at your chambers to return your diary.
“I remember that as I entered the room and cast my eyes over the
things that were spread out on the table, I received quite a shock.
For the first glance showed me that, amongst those things were two
objects that exactly fulfilled the conditions of the final test. There
was the wax mould—a part, and the greater part, of one of the
suspected candles; and there was the tress of hair—a portion of the
body of the person suspected to have been poisoned. With these two
objects it was possible to determine with absolute certainty whether
that person had or had not been poisoned with arsenic, and if she had,
whether the candle had or had not been the medium by which the poison
was administered.”
“But,” I said, “you knew from the diary of the existence of the wax
mould.”
“I knew that it _had_ existed. But I naturally supposed that the cast
had been taken and the mould destroyed years ago, though I had
intended to ask you about it. However, here it was, miraculously
preserved, against all probabilities, still awaiting completion. Of
course, I recognized it instantly, and began to cast about in my mind
for some means of making the necessary examination without disclosing
my suspicions. For you will realize that I was unwilling to say
anything to you about Stella’s death until the question was settled
one way or the other. If the examination had shown no arsenic either
in the candle or in the hair, it would not have been necessary to say
anything to you at all.
“But while I was debating the matter, the problem solved itself. As
soon as I came to look at Stella’s unfinished works, I saw that they
cried aloud to be completed and that Polton was the proper person to
carry out the work. I made the suggestion, which I should have made in
any case, and when you adopted it, I decided to say nothing but to
apply the tests when the opportunity offered.”
“I am glad,” said I, “to hear you say that you would have made the
suggestion in any case. It looked at first like a rather cold-blooded
pretext to get possession of the things. But you were speaking of the
hair. Can you depend on finding recognizable traces of arsenic in the
hair of a person who has been poisoned?”
“Certainly, you can,” he replied. “The position is this: When arsenic
is taken it becomes diffused throughout the whole body, including the
blood, the bones and the skin. But as soon as a dose of arsenic is
taken, the poison begins to be eliminated from the body, and, if no
further dose is taken, the whole of the poison is thrown off in a
comparatively short time until none remains in the tissues—with one
exception. That exception is the epidermis, or outer skin, with its
appendages—the finger and toe nails and the hair. These structures
differ from all others in that, instead of growing interstitially and
being alive throughout, they grow at a certain growing-point and then
become practically dead structures. Thus a hair grows at the
growing-point where the bulb joins the true skin. Each day a new piece
of hair is produced at the living root, but when once it has come into
being it grows no more, but is simply pushed up from below by the next
portion. Thenceforward it undergoes no change, excepting that it
gradually moves upwards as new portions are added at the root. It is
virtually a dead, unchanging structure.
“Now suppose a person to take a considerable dose of arsenic. That
arsenic becomes diffused throughout all the living tissues and is for
a time deposited in them. The growing point of the hair is a living
tissue and of course the arsenic becomes deposited in it. Then the
process of elimination begins and the arsenic is gradually removed
from the living tissues. But in twenty-four hours, what was the
growing-point of the hair has been pushed up about the fiftieth of an
inch and is no longer a growing structure. It is losing its vitality.
And as it ceases to be a living tissue it ceases to be affected by the
process of elimination. Hence the arsenic which was deposited in it
when it was a living tissue is never removed. It remains as a
permanent constituent of that part of the hair, slowly moving up as
the hair grows from below, until at last it is snipped off by the
barber; or, if the owner is a long-haired woman, it continues to creep
along until the hair is full-grown and drops out.”
“Then the arsenic remains always in the same spot?”
“Yes. It is a local deposit at a particular point in the hair. And
this, Mayfield, is a most important fact, as you will see presently.
For observe what follows. Hair grows at a uniform rate—roughly, a
fiftieth of an inch in twenty-four hours. It is consequently possible,
by measurement, to fix nearly exactly, the age of any given point on a
hair. Thus if we have a complete hair and we find at any point in it a
deposit of arsenic, by measuring from that point to the root we can
fix, within quite narrow limits, the date on which that dose of
arsenic was taken.”
“But is it possible to do this?” I asked.
“Not in the case of a single hair,” he replied. “But in the case of a
tress, in which all the hairs are of the same age, it is perfectly
possible. You will see the important bearing of this presently.
“To return now to my investigation. I had the bulk of a candle and a
tress of Stella’s hair. The questions to be settled were, 1. Was there
arsenic in the candle? and 2. Had Stella been poisoned with arsenic? I
began by trimming the wax mould in readiness for casting and then I
made an analysis of the trimmings. The result was the discovery of
considerable quantities of arsenic in the wax.
“That answered the first question. Next, as the tress of hair was
larger than was required for your purpose, I ventured to sacrifice a
portion of it for a preliminary test. That test also gave a positive
result. The quantity of arsenic was, of course, very minute, but still
it was measurable by the delicate methods that are possible in dealing
with arsenic; and the amount that I found pointed either to one large
dose or to repeated smaller ones.
“The two questions were now answered definitely. It was certain—and
the certainty could be demonstrated to a jury—that Stella had been
poisoned by arsenic, and that the arsenic had been administered by
means of poisoned candles. The complete proof in this case lent added
weight to the less complete proof in the case of Monkhouse; and the
two cases served to corroborate one another in pointing to Barbara as
the poisoner. For she was the common factor in the two cases. The
other persons—Wallingford, Madeline and the others—who appeared in the
Monkhouse case, made no appearance in the case of Stella; and the
persons who were associated with Stella were not associated with
Monkhouse. But Barbara was associated with both. And her absence from
home was no answer to the charge if death was caused by the candles
which she had admittedly supplied.
“But complete as the proof was, I wished, if possible, to make it yet
more complete: to associate Barbara still more definitely with the
crime. In the case of Monkhouse, it was clear that the poisoning
always occurred when she was absent from home. But this was not so
clear in the case of Stella. Your diary showed that Stella’s relapses
coincided pretty regularly with Barbara’s absences; but it was not
certain (though obviously probable) that the relapses coincided with
the periods of poisoning. If it could be proved that they did
coincide, that proof would furnish corroboration of the greatest
possible weight. It would show that the two cases were parallel in all
respects.
“But could it be proved? If the tress of Stella’s hair had been at my
disposal, I had no doubt that I could have decided the question. But
the tress was yours, and it had to be preserved. Whatever was to be
done must be done without destroying or injuring the hair, and I set
myself the task of finding some practicable method. Eventually, I
decided, without much hope of success, to try the X-rays. As arsenic
is a fairly dense metal and the quantity of it in the deposits quite
considerable, it seemed to me possible that it might increase the
density of the hairs at those points sufficiently to affect the X-ray
shadow. At any rate, I decided to give the method a trial.
“Accordingly, Polton and I set to work at it. First, in order to get
the densest shadow possible, we made the tress up into a close
cylinder, carefully arranging it so that all the cut ends were in
exactly the same plane. Then we made a number of graduated exposures
on ‘process’ plates, developing and intensifying with the object of
getting the greatest possible degree of contrast. The result was
unexpectedly successful. In the best negative, the shape of the tress
was faintly visible and was soon to be crossed by a number of
perfectly distinct pale bands. Those bands were the shadows of the
deposits of arsenic. There could be no doubt on the subject. For,
apart from the fact that there was nothing else that they could be,
their appearance agreed exactly with what one would have expected.
Each band presented a sharp, distinct edge towards the tips of the
hairs and faded away imperceptibly towards the roots. The sharp edge
corresponded to the sudden appearance of arsenic in the blood when the
poisoning began. The gradual fading away corresponded to the period of
elimination when the poisoning had ceased and the quantity of arsenic
in the blood was becoming less and less from day to day.
“Now, since hair grows at a known, uniform rate, it was possible to
convert the distances between these arsenical bands into periods of
time; not with perfect exactness, because the rate of growth varies
slightly in different persons, but with sufficient exactness for our
present purpose. As soon as I looked at those bands, I saw that they
told the whole story. But let us follow the method of proof.
“Assuming the rate of growth to be one fiftieth of an inch in
twenty-four hours—which was probably correct for a person of Stella’s
age—I measured off on the photograph seven inches and a quarter from
the cut ends as representing the last year of her life. Of course, I
did not know how close to the head the hair had been cut, but, judging
by the bands, I assumed that it had been cut quite close to the
skin—within a quarter of an inch.”
“I happen to know that you were quite right,” said I, “but I can’t
imagine how you arrived at your conclusion.”
“It was quite a simple inference,” he replied, “as you will see,
presently. But to return to the photograph. Of the measured space of
seven inches and a quarter I took a tracing on sheet celluloid,
marking the sharp edges of the bands, the points at which the fading
began and the points at which the band ceased to be visible. This
tracing I transferred to paper ruled in tenths of an inch—a tenth of
an inch representing five days—and I joined the points where the
fading began and ended by a sloping line. I now had a diagram, or
chart, which showed, with something approaching to accuracy, the
duration of each administration of arsenic and the time which elapsed
between the successive poisonings. This is the chart. The sloping
lines show the fading of the bands.”
He handed me a paper which he had just taken from a drawer and I
looked at it curiously but with no great interest. As I returned it
after a brief inspection I remarked:
“It is quite clear and intelligible, but I don’t quite see why you
took the considerable trouble of making it. Does it show anything that
could not be stated in a few words?”
“Not by itself,” he replied. “But you remember that I mentioned having
made two other charts, one showing the fluctuations in Stella’s
illness and the other showing Barbara’s absences from home during the
same period. Here are those other two charts; and now, if you put the
three together, your eye can take in at a glance a fact of fundamental
importance; which is that the relapses, the absences and the
poisonings all coincided in time. The periodicity is strikingly
irregular; but it is identical in all three charts. I made these to
hand to the jury, and I think they would have been quite convincing,
since any juryman could check them by the dates given in evidence, and
by inspection of the radiograph of the hair.”
[Illustration: Three charts, labelled “A,” “B,” and “C,” each marked
horizontally with the names of months. Charts A and B
are line graphs, while Chart C marks off certain periods of time
with solid blocks. Each chart shows five peaks occurring at the same
points in time.]
Explanation of the Charts
Chart A shows the fluctuations in the illness of Stella Keene during
the year preceding her death in October. Divided into intervals of
five days.
Chart B shows the distribution of the arsenical bands in Stella
Keene’s hair. The steep sides of the curves, towards the tips of the
hairs, show the sudden appearance of the deposit, and the sloping
sides, towards the roots of the hairs, represent its more gradual
fading. Each of the narrow divisions represents five days’ growth.
Chart C shows the periods during which Barbara was absent from home,
each absence being represented by a black column. Divided into
intervals of five days.
I gazed at the three charts and was profoundly impressed by the
convincing way in which they demonstrated the connection between
Barbara’s movements and the results of her diabolical activities. But
what impressed me still more was the amazing ingenuity with which
Thorndyke had contrived to build up a case of the most deadly
precision and completeness out of what seemed, even to my trained
intelligence, no more than a few chance facts, apparently quite
trivial and irrelevant.
“It seems,” I said, “that, so far as you were concerned, the
exhumation was really unnecessary.”
“Quite,” he replied. “It proved nothing that was not already certain.
Still, the Commissioner was quite right. For the purposes of a trial,
evidence obtained from the actual body of the victim is of
immeasurably more weight than indirect scientific evidence, no matter
how complete. An ordinary juryman might have difficulty in realizing
that the hair is part of the body and that proof of arsenical deposit
in the hair is proof of arsenic in the body. But the mistake that he
made, as events turned out, was in refusing to make the arrest until
my statements had been confirmed by the autopsy and the analysis. That
delay allowed the criminal to escape. Not that I complain. To me,
personally, her suicide came as a blessed release from an almost
intolerable position. But if I had been in his place, I would have
taken no chances. She would have gone to trial and to the gallows.”
“Yes,” I admitted; “that was what justice demanded. But I cannot be
thankful enough for the delay that let her escape. Fiend as she was,
it would have been a frightful thing to have had to give the evidence
that would have hanged her.”
“It would,” he agreed; “and the thought of it was a nightmare to me.
However, we have escaped that; and after all, justice has been done.”
We were silent for a few minutes, during which Thorndyke smoked his
pipe with a certain air of attention as if he expected me to put some
further questions. And, in fact, there were one or two questions that
I wanted to have answered. I began with the simplest.
“I am still a little puzzled by some of the circumstances in this
case. The infernal machine I happen to know to have been sent by
Barbara, though I don’t understand why she sent it. But Wallingford’s
proceedings are a complete mystery to me. What do you suppose induced
him to keep a watch on you in that extraordinary fashion? And who was
the man who shadowed him? There certainly was such a man, for I saw
him, myself. And the same man had been shadowing Miss Norris. What do
you make of it all?”
“One can only reason from past experiences,” he replied. “It seems to
be a rule that a person who has committed a crime cannot remain quiet
and let things take their course. There appears to be an irresistible
impulse to lay down false clues and create misleading appearances. It
is always a mistake, unless the false clues are laid down in advance,
and even then it is apt to fail and unexpectedly furnish a real clue.
“Now Barbara, with all her astonishing cleverness, made that mistake.
She laid down a false clue in advance by her absences from home, and
the trick certainly worked successfully at the inquest. But it was
precisely those absences that put me on the track of the candle, which
otherwise might have passed unsuspected. The faked medicine was
another false clue which attracted my attention and added to my
suspicion concerning the candle. Then, after the event came these
other endeavours to mislead. They did neither harm nor good, as it
happened, since I had already marked her down as the principal
suspect. But if I had been in doubt, I should have followed up those
clues and found her at the end of them.
“As to Wallingford, I imagine that she led him to believe that I was
employed by you to fix the crime on him and that he was advised to
watch me and be ready to anticipate any move on my part; her actual
object being to cause him to behave in such a manner as to attract
suspicious attention. The function of the private detective—for that
is what he must have been—would be to keep Wallingford’s nerves—and
Miss Norris’s, too—in such a state that they would appear anxious and
terrified and tend to attract attention. The infernal machine was
primarily intended, I think, to cast suspicion on one or both of them.
That was what I inferred from the total absence of finger-prints and
the flagrantly identifiable character of the pistol and the wool.
“But the greatest, the most fatal mistake that Barbara made was the
one that is absolutely characteristic of the criminal. She repeated
the procedure of a previous crime that had been successful. It was
that repetition that was her undoing. Either crime, separately, might
have been difficult to fix on her. As it was, each crime was proof of
the other.”
Once more we fell silent; and still Thorndyke had the air of expecting
some further question from me. I looked at him nervously; for there
was something that I wanted to ask and yet I hardly dared to put it
into words. For, as I had looked at those charts, a horrid suspicion
had taken hold of me. I feared to have it confirmed, and yet I could
not let it rest. At last, I summoned courage enough to put the
question.
“Thorndyke,” I said, “I want you to tell me something. I expect you
know what it is.”
He looked up and nodded gravely.
“You mean about Stella?” said he.
“Yes. How long would she have lived if she had not been poisoned?”
He looked away for a few moments, and, impassive as his face was, I
could see that he was deeply moved. At length he replied:
“I was afraid you were going to ask me that. But since you have, I can
only answer you honestly. So far as I can judge, but for that accursed
ghoul, the poor girl might have been alive and well at this moment.”
I stared at him in amazement. “Do you mean,” I demanded, “that she was
not really suffering from consumption at all?”
“That is what it amounts to,” he replied. “There were signs of old
tubercular trouble, but there was nothing recent. Evidently she had
good powers of resistance, and the disease had not only become
stationary, but was practically extinct. The old lesions had undergone
complete repair, and there is no reason to suppose that any recurrence
would have taken place under ordinary conditions.”
“But,” I exclaimed, hardly able to believe that the disaster had been
so overwhelmingly complete, “what about the cough? I know that she
always had a more or less troublesome cough.”
“So had Monkhouse,” he replied; “and so would any one have had whose
lungs were periodically irritated by inhaling particles of arsenious
acid. But the tubercular mischief was quite limited and recovery must
have commenced early. And Barbara, watching eagerly the symptoms of
the disease which was to rid her of her rival, must have noted with
despair the signs of commencing recovery and at last resolved to do
for herself what nature was failing to do. Doubtless, the special
method of poisoning was devised to imitate the symptoms of the
disease; which it did well enough to deceive those whose minds were
prepared by the antecedent illness to receive the suggestion. It was a
horribly, fiendishly ingenious crime; calmly, callously devised and
carried out to its appalling end with the most hideous efficiency.”
After he had finished speaking, I remained gazing at him dumbly,
stupefied, stunned by the realization of the enormity of this
frightful thing that had befallen. He, too, seemed quite overcome, for
he sat silently, grasping his extinct pipe and looking sternly and
fixedly into the fire. At length he spoke, but without removing his
gaze from the bright embers.
“I am trying, Mayfield,” he said, gently, “to think of something to
say to you. But there is nothing to say. The disaster is too complete,
too irretrievable. This terrible woman has, so far, wrecked your life,
and I recognize that you will carry the burden of your loss so long as
you live. It would be a mere impertinence to utter futile and banal
condolences. You know what I, your friend, am feeling and I need say
no more of that; and I have too much confidence in your wisdom and
courage to think of exhortations.
“But, though you have been robbed of the future that might have been,
there is still a future that may be. It remains to you now only to
shoulder your fardel and begin your pilgrimage anew; and if the road
shall seem at first a dreary one, you need not travel it alone. You
have friends; and one of them will think it a privilege to bear you
company and try to hearten you by the way.”
He held out his hand and I grasped it silently and with a full heart.
And the closer friendship that was inaugurated in that hand-clasp has
endured through the passing years, ever more precious and more
helpful.
The End
Transcriber’s Note
This transcription follows the text of the first edition published by
Dodd, Mead & Company in 1928. However, the following alterations have
been made to correct what are believed to be unambiguous errors in the
text:
* Three occurrences of mismatched quotation marks have been fixed.
* “plainsclothes” has been changed to “plainclothes” (Chapter III).
* “numbers of others” has been changed to “number of others”
(Chapter VIII).
* “attracts” has been changed to “attract” (Chapter X).
* “less that” has been changed to “less than” (Chapter XVI).
* “thier” has been changed to “their” (Chapter XI).
* “quote practicable” has been changed to “quite practicable”
(Chapter XVII).
* “the prisoner” has been changed to “the poisoner” (Chapter XVII).