On a table in a corner by the window stood a microscope which Cushing evidently used, and near it a box of fresh sterilised slides.  Kennedy, who had been casting his eye carefully about taking in the whole laboratory, seemed delighted to find the slides.  He opened the box and gingerly took out some of the little oblong pieces of glass, on each of which he dropped a couple of minute drops of blood from the arterial spurts and the venous pools on the floor.

Near the workbench were circular marks, much as if some jars had been set down there.  We were watching him, almost in awe at the matter of fact manner in which, he was proceeding in what to us was nothing but a hopeless enigma, when I saw him stoop and pick up a few little broken pieces of glass.  There seemed to be blood spots on the glass, as on other things, but particularly interesting to him.

A moment later I saw that he was holding in his hand what were apparently the remains of a little broken vial which he had fitted together from the pieces.  Evidently it had been used and dropped in haste.

“A vial for a local anesthetic,” he remarked.  “This is the sort of thing that might be injected into an arm or leg and deaden the pain of a cut, but that is all.  It wouldn’t affect the consciousness or prevent any one from resisting a murderer to the last.  I doubt if that had anything directly to do with his death, or perhaps even that this is Cushing’s blood on it.”

Unlike Winslow I had seen Kennedy in action so many times that I knew it was useless to speculate.  But I was fascinated, for the deeper we got into the case, the more unusual and inexplicable it seemed.  I gave that end of it up, but the fact that Strong had gone to secure the combination of the safe suggested to me to examine that article.  There was certainly no evidence of robbery or even of an attempt at robbery there.

“Was any doctor called?” asked Kennedy.

“Yes,” he replied.  “Though I knew it was of no use I called in Dr. Howe, who lives up the street from the laboratory.  I should have called Dr. Harris, who used to be my own physician, but since his return from Africa with the Borland expedition, he has not been in very good health and has practically given up his practice.  Dr. Howe is the best practising physician in town, I think.”

“We shall call on him to-morrow,” said Craig, snapping his watch, which already marked far after midnight.  Dr. Howe proved, the next day, to be an athletic-looking man, and I could not help noticing and admiring his powerful frame and his hearty handshake, as he greeted us when we dropped into his office with a card from Winslow.

The doctor’s theory was that Cushing had committed suicide.

“But why should a young man who had invented a new method of polymerising isoprene, who was going to become wealthy, and was engaged to a beautiful young girl, commit suicide?”

The doctor shrugged his shoulders.  It was evident that he, too, belonged to the “natural rubber set” which dominated Goodyear.