As for Kennedy, he was interested in nothing but the problem before him.  He had been strangely quiet on the way, growing more and more impatient and nervous, as though the element of time had entered into the case, as though haste were suddenly imperative.  Once the lights were on in the laboratory he hurried about his various preparations.  The food samples he laid out, but he gave them no attention.  The blood smears and stomach contents he put aside for future reference.  His attack was upon the drop or two of liquid adhering to the stem of the broken champagne glass.

The entire chemical procedure seemed to be incomprehensible to Mackay and he was fascinated, so that he had considerable trouble at times keeping out of the way of Kennedy’s elbow.  Kennedy first washed the stem out carefully with a few drops of distilled water, then he studied the resulting solution.  One after another he tried the things that occurred to him, making tests wholly unproductive of results.  Slowly the laboratory table became littered completely with chemicals and apparatus of all sorts, a veritable arsenal of glass.

The sandwiches arrived, but Kennedy refused to drop his investigation for a moment.  I did succeed in making him take a cup of strong coffee, and that was all.  Over in a corner Mackay and I did full justice to the food, finishing the hot and welcome coffee and then refilling the percolator and starting it on the making of a second brew.  The hours lengthened, and when Mackay grew tired of watching with intense admiration he joined me in the patient consumption of innumerable cigarettes.

Kennedy was filled with the joy of discovery.  I noticed that he did not stop even for the solace of tobacco.  It seemed to me that at times his nostrils dilated exactly like those of a hound on the scent.  Finally he held up a test tube and turned to us.

“What is it?” I asked.  “Some other poison as rare and little known as the snake venom?”

“No—­something much more curious.  In the stem of the glass I find the toxin of the Bacillus botulinus.”

“Germs?” Mackay inquired.

Kennedy shook his head.  “Not germs, but the pure toxin, the poison secreted by this bacillus.”

“What does it do?” was my question.

“Well,” thoughtfully, “botulism may be ranked easily among the most serious diseases known to medical science.  It is hard to understand why it is not a great deal more common.  It is one of the most dangerous kinds of food poisoning.”

“Then the apple juice they used for the wine was bad, spoiled?”

“No, not that.  Werner was the only one stricken.  Somebody put the pure toxin in his glass.  It was, as I suspected, deliberate murder, as in the case of Miss Lamar.  Bacillus botulinus produces a toxin that is extremely virulent.  Hardly more than a ten-thousandth of a cubic centimeter would kill a guinea pig.  This was botulin itself, the pure toxin, an alkaloid just like that which is formed in meat and other food products in cases of botulism.  The idea might also have been to make the death seem natural—­due solely to bad food.”