“Then you think it contained——­” began Jack.

“I’m not going to think anything until I finish this experiment,” laughed Tom.

He shook the sterilized water about in the bottle, rinsing it well, and the contents he then poured into a test tube.  This, after heating, he mixed with some other chemicals.

“Would you mind telling us what you’re testing for?” asked Jack.

“Not at all,” said Tom quietly.  “I’m trying to see if this bottle had any cyanide of potassium in it.”

“What!  Cyanide?” gasped Bert.

“The stuff that killed the one horse and sickened the others?” asked Jack.

“That’s it.  I may find it—­I may not.”

Tom poured a few drops of another chemical into the test tube.  There was a reaction, and at once he uttered a cry: 

“There it is!” he fairly shouted.  “I’m on the right trail at last!  There was cyanide in the bottle!”

“There sure was,” agreed Jack, who had seen the same test made in one of the classes a few days before.

“But I don’t see what good that is,” remarked Bert.  “Everyone knew that cyanide was used on the horses.  It’s a common enough poison.  Naturally whoever used it would have it in a bottle.  Then you accidentally find the bottle in the stable, but that doesn’t tell you who dropped it there.”

“No, but this may,” said Tom quietly, taking a small piece of paper from his pocket and smoothing it out on the table.

“What is it?” asked Jack, and then, before he could be answered he added.  “Oh, I see, part of a druggist’s label.”

“Yes,” admitted Tom.  “It was near the bottle.  It had been washed off, I imagine.  I didn’t show it to you at first, for I wanted to make sure of what the bottle had contained.”

“And now that you’re sure,” began Bert, “I suppose------”

“I’m going to the druggist who sold this, and ask if he can remember who bought it,” went on Tom, for, though the label from the bottle was torn, there was enough of it left to show part of the firm name.  And, as there were but three drug shops in Elmwood, it was not difficult to pick out the one represented.

“We’ll go with you!” exclaimed Jack.  “Hurray, Tom!  I do believe you’re on the trail at last.”

“Sure,” assented Bert.  “Let’s go at once.”

“I’d like to have you along,” explained Tom, “but I think maybe I’d better go by myself.  I’ve got to go at this thing quietly, and if three of us trooped in the drug store, and began asking questions, it would make a scene.  Besides, lots of our fellows hang out there for soda, and they’d see us.  I don’t want this talked about until I get it a little more cleared up.  I don’t want you fellows to feel that------”

“Oh get out!” interrupted Jack.  “You do just as you please, Tom, and we’ll fill in, or play wherever you want us.  This is your game, anyhow, though we want to help you all we can.  Just say the word.”