“Like many barbarians,” continued Craig, “the Ainus from time immemorial have prepared virulent poisons with which they charged their weapons of the chase and warfare.  The formulas for the preparations, as in the case of other arrow poisons of other tribes, are known only to certain members, and the secret is passed down from generation to generation as an heirloom, as it were.  But in this case it is no longer a secret.  It has now been proved that the active principle of this poison is aconite.”

“If that is the case,” broke in Doctor Leslie, “it is hopeless to connect anyone directly in that way with these murders.  There is no test for aconitin.”

I thought Sato’s face was more composed and impassive than ever.  Doctor Bernardo, however, was plainly excited.

“What—­no test—­none?” asked Kennedy, leaning forward eagerly.  Then, as if he could restrain the answer to his own question no longer, he shot out:  “How about the new starch test just discovered by Professor Reichert, of the University of Pennsylvania?  Doubtless you never dreamed that starch may be a means of detecting the nature of a poison in obscure cases in criminology, especially in cases where the quantity of poison necessary to cause death is so minute that no trace of it can be found in the blood.

“The starch method is a new and extremely inviting subject to me.  The peculiarities of the starch of any plant are quite as distinctive of the plant as are those of the hemoglobin crystals in the blood of an animal.  I have analyzed the evidence of my microscope in this case thoroughly.  When the arrow poison is introduced subcutaneously—­say, by a person shooting a poisoned dart, which he afterward removes in order to destroy the evidence--the lethal constituents are rapidly absorbed.

“But the starch remains in the wound.  It can be recovered and studied microscopically and can be definitely recognized.  Doctor Reichert has published a study of twelve hundred such starches from all sorts of plants.  In this case, it not only proves to be aconitin but the starch granules themselves can be recognized.  They came from this piece of arrow poison.”

Every eye was fixed on him now.

“Besides,” he rapped out, “in the soft soil beneath the window of Professor Northrop’s room, I found footprints.  I have only to compare the impressions I took there and those of the people in this room, to prove that, while the real murderer stood guard below the window, he sent some one more nimble up the rain pipe to shoot the poisoned dart at Professor Northrop, and, later, to let down a rope by which he, the instigator, could gain the room, remove the dart, and obtain the key to the treasure he sought.”

Kennedy was looking straight at Professor Bernardo.

“A friend of mine in Mexico has written me about an inscription,” he burst out.  “I received the letter only to-day.  As nearly as I can gather, there was an impression that some of Northrop’s stuff would be valuable in proving the alleged kinship between Mexico and Japan, perhaps to arouse hatred of the United States.”