“Our poisons and our drugs,” he began, leisurely, at length, “are in many instances the close relatives of harmless compounds that represent the intermediate steps in the daily process of metabolism.  There is much that I might say about protein poisons.  However, that is not exactly what I want to talk about—­at least first.”

He stopped to make sure that he had the attention of us all.  As a matter of fact, his manner was such that he attracted even the vagrant interest of the Wardlaws.

“I do not know how much of his suspicions Commissioner Leslie has communicated to you,” he resumed, “but I believe that you have all heard of the disease beriberi so common in the Far East and known to the Japanese as kakke.  It is a form of polyneuritis and, as you doubtless know, is now known to be caused, at least in the Orient, by the removal of the pericarp in the polishing of rice.  Our milling of flour is, in a minor degree, analogous.  To be brief, the disease arises from the lack in diet of certain substances or bodies which modern scientists call vitamines.  Small quantities of these vital principles are absolutely essential to normal growth and health and even to life itself.  They are nitrogenous compounds and their absence gives rise to a class of serious disorders in which the muscles surrender their store of nitrogen first.  The nerves seems to be the preferred creditors, so to speak.  They are affected only after the muscles begin to waste.  It is an abstruse subject and it is not necessary for me to go deeper into it now.”

I controlled my own interest in order to watch those about me.  Kato, for one, was listening attentively, I saw.

“In my studies of the diet of this household,” continued Kennedy, “I have found that substances have been used in preparing food which kill vitamines.  In short, the food has been denatured.  Valuable elements, necessary elements, have been taken away.”

“I, sir, not always in kitchen, sir,” interrupted Kato, still deferential.  “I not always know—­”

With a peremptory wave of his hand Kennedy silenced the Jap.

“It has long been a question,” he hurried on, “whether these vitamines are tangible bodies or just special arrangements of molecules.  Recently government investigators have discovered that they are bodies that can be isolated by a special process from the filtrate of brewer’s yeast by Lloyd’s reagent.  Five grams of this”—­he held up some of the tablets he had made—­“for a sixty-kilogram person each day are sufficient.  Unknown to you, I have introduced some of this substance into the food already deficient in vitamines.  I fancy that even now I can detect a change,” he nodded toward Mrs. Wardlaw.

There was a murmur of surprise in the room, but before Craig could continue further the door opened and Mrs. Wardlaw uttered a nervous exclamation.  There stood Chase with a woman.  I recognized her immediately from Kennedy’s description as Miss Hackstaff.