ising the taste of strychnine that it is extraordinary
no one has thought of it?" Poirot looked round the room, and then
answered himself impressively. "Her medicine!"

"Do you mean that the murderer introduced the strychnine into her
tonic?" I cried.

"There was no need to introduce it. It was already there--in the
mixture. The strychnine that killed Mrs. Inglethorp was the identical
strychnine prescribed by Dr. Wilkins. To make that clear to you, I
will read you an extract from a book on dispensing which I found in the
Dispensary of the Red Cross Hospital at Tadminster:

"'The following prescription has become famous in text books:
Strychninae Sulph. . . . . . gr.I
Potass Bromide . . . . . . . 3vi Aqua
ad. . . . . . . . . . . 3viii Fiat
Mistura

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!"

"Now there was, of course, no bromide in Dr. Wilkins' prescription, but
you will remember that I mentioned an empty box of bromide powders.
One or two of those powders introduced into the full bottle of medicine
would effectually precipitate the strychnine, as the book describes,
and cause it to be taken in the last dose. You will learn later that
the person who usually poured out Mrs. Inglethorp's medicine was always
extremely careful not to shake the bottle, but to leave the sediment at
the bottom of it undisturbed.

"Throughout the case, there have been evidences that the tragedy was
intended to take place on Monday evening. On that day, Mrs. Inglethorp's
bell wire was neatly cut, and on Monday evening Mademoiselle Cynthia was
spending the night with friends, so that Mrs. Inglethorp would have
been quite alone in the right wing, completely shut off from help of any
kind, and would have died, in all probability, before medical aid could
have been summoned. But in her hurry to be in time for the village
entertainment Mrs. Inglethorp forgot to take her medicine, and the next
day she lunched away from home, so that the last--and fatal--dose was
actually taken twenty-four hours later than had been anticipated by the
murderer; and it is owing to that delay that the final proof--the last
link of the chain--is