I slept late in the morning, so that Kennedy had to wake me. When we had finished breakfast he led the way to the laboratory, all without making any effort to satisfy my curiosity. There he started packing up the tubes and materials he had been studying in the case, rather than resuming his investigations.

"What's the idea?" I asked, finally, unable to contain myself any longer.

"You carry this package," he directed. "I'll take the other."

I obeyed, somewhat sulkily I'm afraid.

"You see," he added, as we left the building and hurried to the taxi stand near the campus, "the next problem is to identify the particular kind of venom that was used. Besides, I want to know the nature of the spots on the towel you found. They certainly were not of venom. I have my suspicions what they really are."

He paused while we selected a vehicle and made ourselves comfortable. "To save time," he went on, "I thought I'd just go over to the Castleton Institute. You know in their laboratories the famous Japanese investigator, Doctor Nagoya, has made some marvelous discoveries concerning the venom of snakes. It is his specialty, a matter to which he has practically devoted his life. Therefore I expect that he will be able to confirm certain suspicions of mine very quickly, or"—a shrug—"explode a theory which has slowly been taking form in the back of my head."

When we dismissed the taxi in front of the institute I realized that this would be my first visit to this institution so lavishly endowed by the multi-millionaire, Castleton, for the advancement of experimental science. Kennedy's card, sent in to Doctor Nagoya, brought that eminent investigator out personally to see us. He was the very finest type of Oriental savant, a member of the intellectual nobility of the strange Eastern land only recently made receptive to the civilization of the West. When he and Kennedy chatted together in low tones for a few moments it was hard for me to grasp that each belonged to a basic race strain fundamentally different from the other. East and West had met, upon the plane of modern science. The two were simply men of specialized knowledge, the Japanese pre-eminent in one field, Kennedy in another.

Carefully and thoroughly Kennedy and Nagoya went over the results which Kennedy had already obtained. After a moment Doctor Nagoya conducted us to his research room.

"Now let me show you," said the Oriental.

In a moment they were deep in the mysteries of an even more minute analysis than Kennedy had made before. I took a turn about the room, finding nothing more understandable than the study holding Kennedy's interest. Though I could not grasp it, curiosity kept me hovering close.

"You see"—Nagoya spoke as he finished the test he was making at the moment—"without a doubt it is crotalin, the venom of the rattlesnake, Crotalus horridus."

"There was no snake actually present," I hastened to explain, breaking in. Then at a glance from Kennedy I stopped, abashed, for all this had been made clear to the scientist.

"It is not necessary," Nagoya replied, turning to me with the politeness characteristic of the East. "Crotalin can be obtained now with fair ease. It is a drug used in a new treatment of epilepsy which is being tried out at many hospitals."

I nodded my thanks, not wanting to interrupt again.

Kennedy pressed on to the next point he wished established. "That was the spot on the portieres. Now the ampulla."

"Also crotalin." Doctor Nagoya spoke positively.

"How about this solution?" Kennedy took from my package the tube with the liquid made from the faint spots on the towel which I had found and which had been our first clue. "It is not crotalin."

The Japanese turned to his laboratory table.

Kennedy muttered some vague suggestions which were too technical for me but which seemed to enable Nagoya to eliminate a great deal of work. The test progressed rapidly. Finally the savant stepped back, regarding the solution with a very satisfied smile.

"It is," he explained, carefully, "some of the very anticrotalus venin which we have perfected right here in the institute."

Kennedy nodded. "I suspected as much." There was great elation in his manner. "You see, I had heard all about your wonderful work."

"Yes!" Nagoya waved his hand around at the wonderfully equipped room, only one detail in the many arrangements for medical research made possible by the generosity of Castleton. "Yes," he repeated, proud of his laboratory, as he well might be, "we have made a great deal of progress in the development of protective sera—antivenins, we call them."

"Are they distributed widely?" Kennedy asked, thoughtfully.

"All over the world. We are practically the only source of supply."

"How do you obtain the serum in quantity?"

"From horses treated with increasing doses of the snake venom."

A question struck me as I remembered the peculiar double action of the poison. "Can you tell me just how the antivenin counteracts the effects of the venom?" I inquired of the savant.

"Surely," he replied. "It neutralizes one of the two elements in the venom, the nervous poison, thus enabling the individual to devote all his vitality to overcoming the irritant poison. It is the nervous poison that is the chief death-dealing agent, producing paralysis of the heart and respiration. We advise all travelers to carry the protective serum if they are likely to be exposed to snake bites."

Kennedy picked up the tube containing the solution made from the towel spots. "This antivenin was your product, doctor?"

"Probably so," was the precise answer.

"Then the purchasers can be identified," I suggested.

"We have no record of ordinary purchasers," Nagoya explained, slowly.

Kennedy was keenly disappointed at that, and showed it. However, he thanked the scientist cordially, and we departed. Outside, he turned to me.

"Do you understand now why the night intruder at Tarrytown did not die—if he is one of our suspects—from the scratch of the needle?"

"You mean he had taken an injection of antivenin before—"

"Exactly! We are dealing with a criminal of diabolical cleverness. Not only did he make all his plans to kill Miss Lamar with the greatest possible care, but he prepared against accident to himself. He was taking no chances. He inoculated himself with a protective serum. The needle of the syringe he used for that purpose he wiped upon the towel you discovered in the washroom."