“I’ll saw the horn off and bring it up to the hotel myself, with the ox-gall,” said Mr. Felton.  “You shall have them in half an hour.”

He was as good as his word, for in half an hour Thorndyke was seated at a small table by the window of our private sitting-room in the Black Bull Hotel.  The table was covered with newspaper, and on it lay the long grey horn and Thorndyke’s travelling-case, now open and displaying a small microscope and its accessories.  The butcher was seated solidly in an armchair waiting, with a half-suspicious eye on Thorndyke for the report; and I was endeavouring by cheerful talk to keep Mr. Stopford from sinking into utter despondency, though I, too, kept a furtive watch on my colleague’s rather mysterious proceedings.

I saw him unwind the bandage and apply the horn to his ear, bending it slightly to and fro.  I watched him, as he scanned the surface closely through a lens, and observed him as he scraped some substance from the pointed end on to a glass slide, and, having applied a drop of some reagent, began to tease out the scraping with a pair of mounted needles.  Presently he placed the slide under the microscope, and, having observed it attentively for a minute or two, turned round sharply.

“Come and look at this, Jervis,” said he.

I wanted no second bidding, being on tenterhooks of curiosity, but came over and applied my eye to the instrument.

“Well, what is it?” he asked.

“A multipolar nerve corpuscle—­very shrivelled, but unmistakable.”

“And this?”

He moved the slide to a fresh spot.

“Two pyramidal nerve corpuscles and some portions of fibres.”

“And what do you say the tissue is?”

“Cortical brain substance, I should say, without a doubt.”

“I entirely agree with you.  And that being so,” he added, turning to Mr. Stopford, “we may say that the case for the defence is practically complete.”

“What, in Heaven’s name, do you mean?” exclaimed Stopford, starting up.

“I mean that we can now prove when and where and how Miss Grant met her death.  Come and sit down here, and I will explain.  No, you needn’t go away, Mr. Felton.  We shall have to subpoena you.  Perhaps,” he continued, “we had better go over the facts and see what they suggest.  And first we note the position of the body, lying with the feet close to the off-side door, showing that, when she fell, the deceased was sitting, or more probably standing, close to that door.  Next there is this.”  He drew from his pocket a folded paper, which he opened, displaying a tiny blue disc.  “It is one of the sequins with which her hat was trimmed, and I have in this envelope several more which I took from the hat itself.

“This single sequin I picked up on the rear end of the off side footboard, and its presence there makes it nearly certain that at some time Miss Grant had put her head out of the window on that side.