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It will be observed in the course of the following lectures that, while the physical signs associated with pectoral disease, especially as relates to phthisis, are not neglected ; yet, as the elucidation of these indications is not the primary object, they are more cursorily noticed than in many modern works relating to such affections. Other manifestations of disease have been more fully discussed ; because, although of special importance in their practical relations, they are perhaps, from various causes, too often inadequately appreciated. Some further notice of the phenomena presented by auscultation

may here be appropriately introduced ; but it would be inexpedient to swell the volume with a systematic and elaborate dissertation, since valuable treatises on the subject are readily accessible. The few introductory remarks now offered are, therefore, chiefly designed to render this branch of science more simple, and more readily comprehensible to the student.

It is gratifying to reflect on the remarkable progress made during the present century in the diagnosis of thoracic disease ; a progress which a glance at standard works published less than thirty years since will render strikingly apparent. It may be sufficient to instance the remarks of Dr. Mason Good, in the second edition of his work on the “Study of Medicine ;" * published about the period when Sir John Forbes first called the attention of the profession in this country to the observations of Laennec. The chapter on Dropsy of the Chest, in Dr. Good's work, may be selected as affording material of much interest, viewed in relation to the present mode of investigation. In reference to dropsy of the mediastinum, pleura, pericardium, and lungs, Dr. Good observes : “ These can never with any degree of certainty be distinguished from each other till after death ;” and “ those who are desirous of examining into the curious and often contradictory signs, by which these several forms of pectoral dropsy have been attempted to be discriminated by various writers, may turn with advantage to Sir J. Maclean's work upon the subject.” He adds,t “The only decisive symptom in this disease is the fluctuation of water in the chest, whenever it can be ascertained ; for several of the other signs are often wanting, or, in a separate state, are to be found in other complaints of the chest, as well as in dropsy, more particularly in asthma and empyema.”

Every reader of these lectures is probably familiar with the change effected in this department of inquiry, since these remarks of Dr. Good were penned. It must however be acknowledged, that the advantages which the new modes of investigation offer have not always been realized; partly in consequence of a tendency to * Vol. v. p. 404.

# Ibid. p. 407.

regard the phenomena observed by means of auscultation as necessarily obscure and complicated. That such an opinion is founded on misapprehension, will be rendered obvious by a little reflection on the physical causes of the acoustic phenomena to which auscultation is applied.

The soft silky sound, heard on listening to the chest of a healthy individual in the act of breathing, cannot be mistaken. Every practitioner must have had frequent occasion to observe this silky murmur superseded by bubbling sounds; when, in consequence of affections of a catarrhal character, the air in its entrance or its exit passes through the secretions with which the air passages are occupied : the sound being necessarily modified according as this secretion is confined to bronchi of considerable calibre, or diffused through the smaller tubes, or the aërating tissue of the lungs. When the smooth expansion of this tissue is prevented by causes extrinsic to the cells, and when the air in expiration does not pass through secreted fluid, the sound produced has not a bubbling character, and may be confined to the period of inspiration. In this way varieties of crackling and crepitation sounds originate. When, in consequence of thickening of the investing membranes, or the presence of any partial obstacle, the calibre of the bronchi is altered, vibratory sounds are induced, which may be grave or acute, according to the diameter of the passages affected.

The simple view thus presented sufficiently represents the principal circumstances which require to be considered, in the practical application of auscultation to those diseases of the chest in which difficulties are

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