XII

never drunk. Yet the strychnine must have been administered between seven and nine o’clock that evening. What third medium was there⁠—a medium so suitable for disguising 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:

“ ‘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.