To the Editor:— I have just noticed the comments by Master inThe Journal, April 22, on coronary thrombosis. It is, of course, hard to get at the facts as to the origin of coronary occlusion from either the experimental or the postmortem approach. In an analysis of 100 private patients carefully studied, I was able to find 17 per cent who had had an occlusion within twenty-four hours of definitely unusual and, frequently, rather extreme exertion. For example, one of my patients, a salesman who was not used to physical strain, had been having stenocardia of effort, although it was not severe. At 6 a. m., with a temperature of 7 degrees below zero, he attempted to crank his car, which had failed to start. After a great deal of strain he did succeed, but in an hour or two he was complaining of some indigestion. At 5 p.