"'The most common form of Daltonism'--that's color-blindness you know, Tommy--'depends on the absence of the red sense. Great additions to our knowledge of this subject, if only in confirmation of results already deduced from theory, have been obtained in the last few years by Holmgren, who has experimented on two persons, each of whom was found to have _one color-blind eye_, the other being nearly normal." "Color-blind!" spluttered the master mechanic. "In one eye," said Carleton, sort of as though he were turning a problem over in his mind. "That would account for it all, Tommy. As far as I know, one doesn't go color-blind--one is born that way--and if this is what's at the bottom of it, Owsley's been color-blind all his life in one eye, and probably didn't know what was the matter. That would account for his passing the tests, and would account for what happened at Elbow Bend. It was the patch that did it--you remember what he said--the light was white as the moon." "And he's out!" stormed Regan. "Out for keeps--after forty years. Say, d'ye know what this'll mean to Owsley--do you, eh, do you? It'll be hell for him, Carleton--he thinks more of his engine than a woman does of her child." Carleton closed the volume and replaced it mechanically in the bookcase. Regan's teeth met in his plug and jerked savagely at the tobacco. "I wish to blazes you hadn't read that!" he muttered fiercely. "What's to be done now?" "I'm afraid there's only one thing to be done," Carleton answered gravely. "Sentiment doesn't let us out--there's too many lives at stake every time he takes out an engine. He'll have to try the color test with a patch over the same eye he had it on that night. Perhaps, after all, I'm wrong, and----" "He's out!" said the master mechanic gruffly. "He's out--I don't need any test to know that now. That's what's the matter, and no other thing on earth. It's rough, damn rough, ain't it--after forty years?"--and Regan, with a short laugh, strode to the window and stood staring out at the choked railroad yards below him. And Regan was right. Three weeks later, when he got out of bed, Owsley took the color test under the queerest conditions that ever a railroad man took it--with his right eye bandaged--and failed utterly.