We dined leisurely, which seemed strange to me, for it was not
Kennedy's custom to let moments fly uselessly when he was on a case.
However, I soon found out why it was. He was waiting for darkness.

As soon as the lights began to glow in the little stores on the main street, we sallied forth, taking the direction of the Pearcy and Minturn houses.

On the way he dropped into the hardware store and purchased a light spade and one of the small pocket electric flashlights, about which he wrapped a piece of cardboard in such a way as to make a most effective dark lantern.

We trudged along in silence, occasionally changing from carrying the heavy package to the light spade.

Both the Pearcy and Minturn houses were in nearly total darkness when we arrived. They set well back from the road and were plentifully shielded by shrubbery. Then, too, at night it was not a much frequented neighborhood. We could easily hear the footsteps of anyone approaching on the walk, and an occasional automobile gliding past did not worry us in the least.

"I have calculated carefully from an examination of the water company's map," said Craig, "just where the water pipe of the two houses branches off from the main in the road."

After a measurement or two from some landmark, we set to work a few feet inside, under cover of the bushes and the shadows, like two grave diggers.

Kennedy had been wielding the spade vigorously for a few minutes when it touched something metallic. There, just beneath the frost line, we came upon the service pipe.

He widened the hole, and carefully scraped off the damp earth that adhered to the pipe. Next he found a valve where he shut off the water and cut out a small piece of the pipe.

"I hope they don't suspect anything like this in the houses with their water cut off," he remarked as he carefully split the piece open lengthwise and examined it under the light.

On the interior of the pipe could be seen patchy lumps of white which projected about an eighth of an inch above the internal surface. As the pipe dried in the warm night air, they could easily be brushed off as a white powder.

"What is it—strychnine?" I asked.

"No," he replied, regarding it thoughtfully with some satisfaction. "That is lead carbonate. There can be no doubt that the turbidity of the water was due to this powder in suspension. A little dissolves in the water, while the scales and incrustations in fine particles are carried along in the current. As a matter of fact the amount necessary to make the water poisonous need not be large."

He applied a little instrument to the cut ends of the pipe. As I bent over, I could see the needle on its dial deflected just a bit.

"My voltmeter," he said, reading it, "shows that there is a current of about 1.8 volts passing through this pipe all the time."

"Electrolysis of water pipes!" I exclaimed, thinking of statements I had heard by engineers. "That's what they mean by stray or vagabond currents, isn't it?"

He had seized the lantern and was eagerly following up and down the line of the water pipe. At last he stopped, with a low exclamation, at a point where an electric light wire supplying the Minturn cottage crossed overhead. Fastened inconspicuously to the trunk of a tree which served as a support for the wire was another wire which led down from it and was buried in the ground.

Craig turned up the soft earth as fast as he could, until he reached the pipe at this point. There was the buried wire wound several times around it.

As quickly and as neatly as he could he inserted a connection between the severed ends of the pipe to restore the flow of water to the houses, turned on the water and covered up the holes he had dug. Then he unwrapped the package which we had tugged about all day, and in a narrow path between the bushes which led to the point where the wire had tapped the electric light feed he placed in a shallow hole in the ground a peculiar apparatus.

As nearly as I could make it out, it consisted of two flat platforms between which, covered over and projected, was a slip of paper which moved forward, actuated by clockwork, and pressed on by a sort of stylus. Then he covered it over lightly with dirt so that, unless anyone had been looking for it, it would never be noticed.

It was late when we reached the city again, but Kennedy had one more piece of work and that devolved on me. All the way down on the train he had been writing and rewriting something.

"Walter," he said, as the train pulled into the station, "I want that published in to-morrow's papers."

I looked over what he had written. It was one of the most sensational stories I have ever fathered, beginning, "Latest of the victims of the unknown poisoner of whole families in Stratfield, Connecticut, is Miss Isabel Pearcy, whose father, Randall Pearcy, died last week."

I knew that it was a "plant" of some kind, for so far he had discovered no evidence that Miss Pearcy had been affected. What his purpose was, I could not guess, but I got the story printed.

The next morning early Kennedy was quietly at work in the laboratory.

"What is this treatment of lead poisoning by electrolysis?" I asked, now that there had come a lull when I might get an intelligible answer. "How does it work?"

"Brand new, Walter," replied Kennedy. "It has been discovered that ions will flow directly through the membranes."

"Ions?" I repeated. "What are ions?"

"Travelers," he answered, smiling, "so named by Faraday from the Greek verb, io, to go. They are little positive and negative charges of electricity of which molecules are composed. You know some believe now that matter is really composed of electrical energy. I think I can explain it best by a simile I use with my classes. It is as though you had a ballroom in which the dancers in couples represent the neutral molecules. There are a certain number of isolated ladies and gentlemen—dissociated ions—" "Who don't know these new dances?" I interrupted.

"They all know this dance," he laughed. "But, to be serious in the simile, suppose at one end of the room there is a large mirror and at the other a buffet with cigars and champagne. What happens to the dissociated ions?"

"Well, I suppose you want me to say that the ladies gather about the mirror and the men about the buffet."

"Exactly. And some of the dancing partners separate and follow the crowd. Well, that room presents a picture of what happens in an electrolytic solution at the moment when the electric current is passing through it."

"Thanks," I laughed. "That was quite adequate to my immature understanding."

Kennedy continued at work, checking up and arranging his data until the middle of the afternoon, when he went up to Stratfield.

Having nothing better to do, I wandered out about town in the hope of running across some one with whom to while away the hours until Kennedy returned. I found out that, since yesterday, Broadway had woven an entirely new background for the mystery. Now it was rumored that the lawyer Minturn himself had been on very intimate terms with Mrs. Pearcy. I did not pay much attention to the rumor, for I knew that Broadway is constitutionally unable to believe that anybody is straight.

Kennedy had commissioned me to keep in touch with Josephson and I finally managed to get around to the Baths, to find them still closed.

As I was talking with him, a very muddy and dusty car pulled up at the door and a young man whose face was marred by the red congested blood vessels that are in some a mark of dissipation burst in on us.

"What—closed up yet—Joe?" he asked. "Haven't they taken Minturn's body away?"

"Yes, it was sent up to Stratfield to-day," replied the masseur, "but the coroner seems to want to worry me all he can."

"Too bad. I was up almost all last night, and to-day I have been out in my car—tired to death. Thought I might get some rest here. Where are you sending the boys—to the Longacre?"

"Yes. They'll take good care of you till I open up again. Hope to see you back again, then, Mr. Pearcy," he added, as the young man turned and hurried out to his car again. "That was that young Pearcy, you know. Nice boy—but living the life too fast. What's Kennedy doing—anything?"

I did not like the jaunty bravado of the masseur which now seemed to be returning, since nothing definite had taken shape. I determined that he should not pump me, as he evidently was trying to do. I had at least fulfilled Kennedy's commission and felt that the sooner I left Josephson the better for both of us.

I was surprised at dinner to receive a wire from Craig saying that he was bringing down Dr. Gunther, Mrs. Pearcy and Isabel to New York and asking me to have Warner Pearcy and Josephson at the laboratory at nine o'clock.

By strategy I managed to persuade Pearcy to come, and as for Josephson, he could not very well escape, though I saw that as long as nothing more had happened, he was more interested in "fixing" the police so that he could resume business than anything else.

As we entered the laboratory that night, Kennedy, who had left his party at a downtown hotel to freshen up, met us each at the door. Instead of conducting us in front of his laboratory table, which was the natural way, he led us singly around through the narrow space back of it.

I recall that as I followed him, I half imagined that the floor gave way just a bit, and there flashed over me, by a queer association of ideas, the recollection of having visited an amusement park not long before where merely stepping on an innocent-looking section of the flooring had resulted in a tremendous knocking and banging beneath, much to the delight of the lovers of slap-stick humor. This was serious business, however, and I quickly banished the frivolous thought from my mind.

"The discovery of poison, and its identification," began Craig at last when we had all arrived and were seated about him, "often involves not only the use of chemistry but also a knowledge of the chemical effect of the poison on the body, and the gross as well as microscopic changes which it produces in various tissues and organs—changes, some due to mere contact, others to the actual chemicophysiological reaction between the poison and the body."

His hand was resting on the poles of a large battery, as he proceeded: "Every day the medical detective plays a more and more important part in the detection of crime, and I might say that, except in the case of crime complicated by a lunacy plea, his work has earned the respect of the courts and of detectives, while in the case of insanity the discredit is the fault rather of the law itself. The ways in which the doctor can be of use in untangling the facts in many forms of crime have become so numerous that the profession of medical detective may almost be called a specialty."

Kennedy repeated what he had already told me about electrolysis, then placed between the poles of the battery a large piece of raw beef.

He covered the negative electrode with blotting paper and soaked it in a beaker near at hand.

"This solution," he explained, "is composed of potassium iodide. In this other beaker I have a mixture of ordinary starch."

He soaked the positive electrode in the starch and then jammed the two against the soft red meat. Then he applied the current.

A few moments later he withdrew the positive electrode. Both it and the meat under it were blue!

"What has happened?" he asked. "The iodine ions have actually passed through the beef to the positive pole and the paper on the electrode. Here we have starch iodide."

It was a startling idea, this of the introduction of a substance by electrolysis.

"I may say," he resumed, "that the medical view of electricity is changing, due in large measure to the genius of the Frenchman, Dr. Leduc. The body, we know, is composed largely of water, with salts of soda and potash. It is an excellent electrolyte. Yet most doctors regard the introduction of substances by the electric current as insignificant or nonexistent. But on the contrary the introduction of drugs by electrolysis is regular and far from being insignificant may very easily bring about death.

"That action," he went on, looking from one of us to another, "may be therapeutic, as in the cure for lead poisoning by removing the lead, or it may be toxic—as in the case of actually introducing such a poison as strychnine into the body by the same forces that will remove the lead."

He paused a moment, to enforce the point which had already been suggested. I glanced about hastily. If anyone in his little audience was guilty, no one betrayed it, for all were following him, fascinated. Yet in the wildly throbbing brain of some one of them the guilty knowledge must be seared indelibly. Would the mere accusation be enough to dissociate the truth from, that brain or would Kennedy have to resort to other means?

"Some one," he went on, in a low, tense voice, leaning forward, "some one who knew this effect placed strychnine salts on one of the electrodes of the bath which Owen Minturn was to use."

He did not pause. Evidently he was planning to let the force of his exposure be cumulative, until from its sheer momentum it carried everything before it.

"Walter," he ordered quickly. "Lend me a hand."

Together we moved the laboratory table as he directed.

There, in the floor, concealed by the shadow, he had placed the same apparatus which I had seen him bury in the path between the Pearcy and Minturn estates at Stratfield.

We scarcely breathed.

"This," he explained rapidly, "is what is known as a kinograph—the invention of Professor HeleShaw of London. It enables me to identify a person by his or her walk. Each of you as you entered this room has passed over this apparatus and has left a different mark on the paper which registers."

For a moment he stopped, as if gathering strength for the final assault.

"Until late this afternoon I had this kinograph secreted at a certain place in Stratfield. Some one had tampered with the leaden water pipes and the electric light cable. Fearful that the lead poisoning brought on by electrolysis might not produce its result in the intended victim, that person took advantage of the new discoveries in electrolysis to complete that work by introducing the deadly strychnine during the very process of cure of the lead poisoning."

He slapped down a copy of a newspaper. "In the news this morning I told just enough of what I had discovered and colored it in such a way that I was sure I would arouse apprehension. I did it because I wanted to make the criminal revisit the real scene of the crime. There was a double motive now—to remove the evidence and to check the spread of the poisoning."

He reached over, tore off the paper with a quick, decisive motion, and laid it beside another strip, a little discolored by moisture, as though the damp earth had touched it.

"That person, alarmed lest something in the cleverly laid plot, might be discovered, went to a certain spot to remove the traces of the diabolical work which were hidden there. My kinograph shows the footsteps, shows as plainly as if I had been present, the exact person who tried to obliterate the evidence."

An ashen pallor seemed to spread over the face of Miss Pearcy, as
Kennedy shot out the words.

"That person," he emphasized, "had planned to put out of the way one who had brought disgrace on the Pearcy family. It was an act of private justice."

Mrs. Pearcy could stand the strain no longer. She had broken down and was weeping incoherently. I strained my ears to catch what she was murmuring. It was Minturn's name, not Gunther's, that was on her lips.

"But," cried Kennedy, raising an accusatory finger from the kinograph tracing and pointing it like the finger of Fate itself, "but the self-appointed avenger forgot that the leaden water pipe was common to the two houses. Old Mr. Pearcy, the wronged, died first. Isabel has guessed the family skeleton—has tried hard to shield you, but, Warner Pearcy, you are the murderer!"