Rapidly he sketched what he had already told me of the thyroid and the hormones.  “These hormones,” added Kennedy, “are closely related to many reactions in the body, such as even the mother’s secretion of milk at the proper time and then only.  That and many other functions are due to the presence and character of these chemical secretions from the thyroid and other ductless glands.  It is a fascinating study.  For we know that anything that will upset--reduce or increase—­the hormones is a matter intimately concerned with health.  Such changes,” he said earnestly, leaning forward, “might be aimed directly at the very heart of what otherwise would be a true eugenic marriage.  It is even possible that loss of sex itself might be made to follow deep changes of the thyroid.”

He stopped a moment.  Even if he had accomplished nothing else he had struck a note which had caused the Athertons to forget their former superciliousness.

“If there is an oversupply of thyroid hormones,” continued Craig, “that excess will produce many changes, for instance a condition very much like exophthalmic goiter.  And,” he said, straightening up, “I find that Eugenia Atherton has within her blood an undue proportion of these thyroid hormones.  Now, is it overfunction of the glands, hyper-secretion—­or is it something else?”

No one moved as Kennedy skillfully led his disclosure along step by step.

“That question,” he began again slowly, shifting his position in the chair, “raises in my mind, at least, a question which has often occurred to me before.  Is it possible for a person, taking advantage of the scientific knowledge we have gained, to devise and successfully execute a murder without fear of discovery?  In other words, can a person be removed with that technical nicety of detail which will leave no clue and will be set down as something entirely natural, though unfortunate?”

It was a terrible idea he was framing, and he dwelt on it so that we might accept it at its full value.  “As one doctor has said,” he added, “although toxicologists and chemists have not always possessed infallible tests for practical use, it is at present a pretty certain observation that every poison leaves its mark.  But then on the other hand, students of criminology have said that a skilled physician or surgeon is about the only person now capable of carrying out a really scientific murder.

“Which is true?  It seems to me, at least in the latter case, that the very nicety of the handiwork must often serve as a clue in itself.  The trained hand leaves the peculiar mark characteristic of its training.  No matter how shrewdly the deed is planned, the execution of it is daily becoming a more and more difficult feat, thanks to our increasing knowledge of microbiology and pathology.”

He had risen, as he finished the sentence, every eye fixed on him, as if he had been a master hypnotist.

“Perhaps,” he said, taking off the cylinder from the phonograph and placing on one which I knew was that which had lain in the library closet over night, “perhaps some of the things I have said will explain or be explained by the record on this cylinder.”