Mr. Mycroft picked up the small tube which he had removed from the fountain pen and which was now standing on a small side-table. “You’ll remember, I said this pippet contains an interesting form of life—a very powerful form, if not itself poisoned. So powerful that, like most power-types, it tends to destroy others, yes, far higher types. This is really a remarkably fecund culture of a particularly virulent strain of typhoid bacillus.”

I drew back. I don’t like things like that near where I eat.

“Oh, it is safe enough so long as you don’t drink it.” I gasped. “So, you see, that was his plan. But, thoughtful man that he was, it was only his second string. He was a very thorough worker and had two concealed tools. If you fall over a bridge headlong and just underneath you is a Nereid holding a charming little wand, there is a good chance that you will fall, like the heroic Roman suicides, on your spear and so end yourself; and if the spear has round its socket some poison, the wound is very likely to give you blood-poisoning. But of course you may miss the point. People falling through the air are apt to writhe which may alter quite considerably the point at which they make their landing, or in this case, their watering. Well, thoughtful Mr. Hess realized how much human nature will struggle against gravitational fate—so he provided himself with a wider net. For when people fall headlong over a bridge, the natural reaction of panic is to open the mouth. So when they strike the water, they inevitably swallow a mouthful. And a little of this brew goes a long way.”

“Now, now,” I broke in, “I don’t think any jury will send the nephew to join the aunt on that evidence.”

“Why not?” was Mr. Mycroft’s unexpectedly quiet rejoinder.

“First,” I said, picking off the points on my fingers just as Mr. Mycroft sometimes does when closing a case, “granted this tube does contain typhoid germs, they may have been in this water from natural pollution. Proof that Hess poisoned the water cannot be sustained. Secondly, let me call the attention of judge and jury to the fact that when Miss Hess died a fortnight after her slight ducking, she did not die of typhoid. The cause of death was ‘intestinal stasis.’ Typhoid kills by a form of dysentery. Emphatically, that condition is polar to stasis.”