"It is a case in point. Theoretically I should have here the innocuous union of three harmless chemicals; as a matter of fact I had occasion to experiment with it and learned that I had innocently produced a vicious and unheard-of poison. The stuff is of no use. It is one of those things a man occasionally stumbles upon in this work,--better forgotten. How do I account for it? I don't. Even in science there is always the unknown element which comes in and plays the devil with results." "But according to your no-waste theory, even this discovery ought to have some use," commented Donaldson with a smile. "Well," drawled the chemist whimsically, "perhaps it has; it makes murder very simple for the laity." "How?" Barstow turned back to his test-tube, relieved that the conversation had taken another turn. "Because of the slowness with which it works. It requires seven days for the system to assimilate it and yet the stomach stubbornly retains it all this while. It is impossible to eliminate it from the body once it is swallowed. It produces no symptoms and leaves no evidence. There is no antidote. In the end it paralyzes the heart--swiftly, silently, surely." Donaldson sat up. "Any pain?" he inquired. "None." Barstow ran his finger over a calendar on the wall. Then he glanced at his watch. "Stay a little while longer and you can see for yourself how it works. I am making a final demonstration of its properties." Barstow stepped into the next room. He was gone five minutes and returned with a scrawny bull terrier scrambling at his heels. The little brute, overjoyed at his release, frisked across the floor, clumsily tumbling over his own feet, and sniffed as an overture of friendship at Donaldson's low shoes. Then wagging his feeble tail he lifted his head and patiently blinked moist eyes awaiting a verdict. The young man stooped and scratched behind its ears, the dog holding his head sideways and pressing against his ankles. He looked like a dog of the streets, but in his eyes there was the dumb appreciation of human sympathy which neutralizes breeding and blood. As Barstow returned to his work, the pup followed after him in a series of awkward bounds. "Poor little pup," murmured Donaldson, sympathetically leaning forward with his arms upon his knees. "What's his name?" "Sandy. But he 's a lucky little pup according to you; within an hour by the clock he ought to be dead." "Dead?" "If my poison works. It was seven days ago to-night that I gave him a dose."