I wish in this paper to make three points: 1. A goodly number of "classic" time-honored mistakes in diagnosis are familiar to all experienced physicians because we make them again and again. Some of these we can avoid; others are almost inevitable, but all should be borne in mind and marked on medical maps by a danger-signal of some kind: "In this vicinity look out for hidden rocks," or "Dangerous turn here, run slow." I shall enumerate some of these danger points presently.
2. Some common diseases are relatively inaccessible to diagnosis, no matter how carefully we are on the watch for them. From the study of 3,000 autopsies, I have begun to work out a percentage or ratio of accessibility for the commoner diseases (shown in the accompanying chart).
3. Besides the classic and well-known pitfalls there are some less familiar to the profession and needing all the more,