Kennedy shook his head.  It was a point that had bothered him a great deal.

“As to the wounds,” he added in a measured tone “although this occurred scarcely three days ago, there is no person even remotely suspected of the crime who can be said to bear on his hands or face others than old scars of wounds.”

He paused.  Then he shot out in quick staccato, “Did you ever hear of Dr. Carrel’s most recent discovery of accelerating the healing of wounds so that those which under ordinary circumstances might take ten days to heal might be healed in twenty-four hours?”

Rapidly, now, he sketched the theory.  “If the factors that bring about the multiplication of cells and the growth of tissues were discovered, Dr. Carrel said to himself, it would perhaps become possible to hasten artificially the process of repair of the body.  Aseptic wounds could probably be made to cicatrise more rapidly.  If the rate of reparation of tissue were hastened only ten times, a skin wound would heal in less than twenty-four hours and a fracture of the leg in four or five days.

“For five years Dr. Carrel has been studying the subject, applying various extracts to wounded tissues.  All of them increased the growth of connective tissue, but the degree of acceleration varied greatly.  In some cases it was as high, as forty times the normal.  Dr. Carrel’s dream of ten times the normal was exceeded by himself.”

Astounded as we were by this revelation, Kennedy did not seem to consider it as important as one that he was now hastening to show us.  He took a few cubic centimetres of some culture which he had been preparing, placed it in a tube, and poured in eight or ten drops of sulphuric acid.  He shook it.

“I have here a culture from some of the food that I found was being or had been prepared for Mr. Pitts.  It was in the icebox.”

Then he took another tube.  “This,” he remarked, “is a one-to-one-thousand solution of sodium nitrite.”

He held it up carefully and poured three or four cubic centimetres of it into the first tube so that it ran carefully down the side in a manner such as to form a sharp line of contact between the heavier culture with the acid and the lighter nitrite solution.

“You see,” he said, “the reaction is very clear cut if you do it this way.  The ordinary method in the laboratory and the text-books is crude and uncertain.”

“What is it?” asked Pitts eagerly, leaning forward with unwonted strength and noting the pink colour that appeared at the junction of the two liquids, contrasting sharply with the portions above and below.

“The ring or contact test for indol,” Kennedy replied, with evident satisfaction.  “When the acid and the nitrites are mixed the colour reaction is unsatisfactory.  The natural yellow tint masks that pink tint, or sometimes causes it to disappear, if the tube is shaken.  But this is simple, clear, delicate—­unescapable.  There was indol in that food of yours, Mr. Pitts.”