In thus rendering my homage to the merits and science of M. Laennec, I do not wish it to be thought, that I consider even his authority as infallible; but it is nothing more than is justly due to the new practice, to admit, that it may become of very great importance; and, that by no other mode can we examine the interior state of the chest, with equal accuracy. Let it be further remarked, that we are not required to lay aside any of our ordinary methods of investigation: This additional mode comes to our aid in cases of obscurity and difficulty. If the physician of long experience be so confident in his powers of diagnosis, that he rejects this invention as unnecessary for his purpose, it need not follow that he should disapprove of it for others who are less experienced, and are more diffident of their skill and penetration. Most assuredly it is a great help to the judgment; and I am fully persuaded, that, in proportion as it is understood, it will be more generally received, and more highly esteemed. If the naked ear be applied to any part of the chest, it is made sensible of the entrance of the air into the cells of the lungs; and the beginner in this study will receive the impression more fully and sensibly, than by the medium of the stethoscope, because the vibrations are collected from a larger surface; but it is a less accurate method, and much less analytical. He may with advantage practise with the naked ear occasionally, in order to become familiar with the sounds of respiration; but under many circumstances, such a mode is inconvenient and inapplicable. The listening by the ear only is technically called, immediate auscultation; and by the stethoscope, mediate auscultation. In examining the chest of a person whose respiration is calm, we should desire that it be made purposely quicker, and stronger; but not so audibly as to cause confusion by that external sound. The perception afforded to the auscultator by healthy lungs, is that of air entering a cavity, as it were with a gentle stream of sound. If the pupil first apply his naked ear to the chest, he will have a clear idea of what he has to expect. As a general rule, in making our investigation of the state of the lungs, the stethoscope should be applied immediately under the clavicle, near the axilla; and the learner will do well to choose the right side, lest he become confused by the action of the heart. In seeking for ordinary respiration, it should not be applied near the trachea, as the stronger action of the air in the bronchial tubes would mislead the ear. To ascertain the state of the posterior part of the lungs, the instrument is to be applied on the scapula, above or below the spinous process.