This is the report of "an investigation of some of the factors concerned in the origin and transmission of some of the sounds heard over the lungs in health and disease." The investigation has been carefully conducted by means of experiments, clinical observation with necropsy control, and a consideration of the laws and theories of physics. The sounds discussed are the voice sounds and the breath sounds as heard in the normal and the consolidated lung, over excavations, pleural effusion and pneumothorax. The book is not intended as a textbook on physical diagnosis. It will interest those who desire to understand more fully the mechanism of the phenomena heard on listening to the normal or diseased lung. It is a pleasure to see the high regard in which the pioneer work of Austin Flint is held, work not always accorded the great credit that it deserves.