It was not a difficult commission, since they did nothing but issue a statement, the net import of which was to let the public know that they were very active, although they had nothing to report.

Kennedy was still busy when I rejoined him, a little late purposely, since I knew that he would be over his head in work.

“What’s this—­a zoo?” I asked, looking about me as I entered the sanctum that evening.

There were dogs and guinea pigs, rats and mice, a menagerie that would have delighted a small boy.  It did not look like the same old laboratory for the investigation of criminal science, though I saw on a second glance that it was the same, that there was the usual hurly-burly of microscopes, test-tubes, and all the paraphernalia that were so mystifying at first but in the end under his skilful hand made the most complicated cases seem stupidly simple.

Craig smiled at my surprise.  “I’m making a little study of intestinal poisons,” he commented, “poisons produced by microbes which we keep under more or less control in healthy life.  In death they are the little fellows that extend all over the body and putrefy it.  We nourish within ourselves microbes which secrete very virulent poisons, and when those poisons are too much for us--well, we grow old.  At least that is the theory of Metchnikoff, who says that old age is an infectious chronic, disease.  Somehow,” he added thoughtfully, “that beautiful white kitchen in the Pitts home had really become a factory for intestinal poisons.”

There was an air of suppressed excitement in his manner which told me that Kennedy was on the trail of something unusual.

“Mouth murder,” he cried at length, “that was what was being done in that wonderful kitchen.  Do you know, the scientific slaying of human beings has far exceeded organised efforts at detection?  Of course you expect me to say that; you think I look at such things through coloured glasses.  But it is a fact, nevertheless.

“It is a very simple matter for the police to apprehend the common murderer whose weapon is a knife or a gun, but it is a different thing when they investigate the death of a person who has been the victim of the modern murderer who slays, let us say, with some kind of deadly bacilli.  Authorities say, and I agree with them, that hundreds of murders are committed in this country every year and are not detected because the detectives are not scientists, while the slayers have used the knowledge of the scientists both to commit and to cover up the crimes.  I tell you, Walter, a murder science bureau not only would clear up nearly every poison mystery, but also it would inspire such a wholesome fear among would-be murderers that they would abandon many attempts to take life.”

He was as excited over the case as I had ever seen him.  Indeed it was one that evidently taxed his utmost powers.

“What have you found?” I asked, startled.