Our next duty was the painful one of breaking the news to Mrs. Northrop.  I shall pass it over.  Perhaps no one could have done it more gently than Kennedy.  She did not cry.  She was simply dazed.  Fortunately her mother was with her, had been, in fact, ever since Northrop had gone on the expedition.

“Why should anyone want to steal tablets of old Mixtec inscriptions?” I asked thoughtfully, as we walked sadly over the campus in the direction of the chemistry building.  “Have they a sufficient value, even on appreciative Fifth Avenue, to warrant murder?”

“Well,” he remarked, “it does seem incomprehensible.  Yet people do just such things.  The psychologists tell us that there is a veritable mania for possessing such curios.  However, it is possible that there may be some deeper significance in this case,” he added, his face puckered in thought.

Who was the mysterious Mexican woman, who the shaggy Russian?  I asked myself.  Clearly, at least, if she existed at all, she was one of the millions not of Spanish but of Indian descent in the country south of us.  As I reasoned it out, it seemed to me as if she must have been an accomplice.  She could not have got into Northrop’s room either before or after Doctor Bernardo left.  Then, too, the toe-and shoe-prints were not hers.  But, I figured, she certainly had a part in the plot.

While I was engaged in the vain effort to unravel the tragic affair by pure reason, Kennedy was at work with practical science.

He began by examining the little dark cylinder on the end of the reed.  On a piece of the stuff, broken off, he poured a dark liquid from a brown-glass bottle.  Then he placed it under a microscope.

“Microscopically,” he said slowly, “it consists almost wholly of minute, clear granules which give a blue reaction with iodine.  They are starch.  Mixed with them are some larger starch granules, a few plant cells, fibrous matter, and other foreign particles.  And then, there is the substance that gives that acrid, numbing taste.”  He appeared to be vacantly studying the floor.

“What do you think it is?” I asked, unable to restrain myself.

“Aconite,” he answered slowly, “of which the active principle is the deadly poisonous alkaloid, aconitin.”

He walked over and pulled down a well-thumbed standard work on toxicology, turned the pages, then began to read aloud: 

Pure aconitin is probably the most actively poisonous substance with which we are acquainted and, if administered hypodermically, the alkaloid is even more powerfully poisonous than when taken by the mouth.

As in the case of most of the poisonous alkaloids, aconitin does not produce any decidedly characteristic post-mortem appearances.  There is no way to distinguish it from other alkaloids, in fact, no reliable chemical test.  The physiological effects before death are all that can be relied on.

Owing to its exceeding toxic nature, the smallness of the dose required to produce death, and the lack of tests for recognition, aconitin possesses rather more interest in legal medicine than most other poisons.