Page:Popular Science Monthly Volume 25.djvu/199

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ONE fifth of the adult population of Christendom is suffering from chest or thoracic diseases of a degree varying from the insignificant to the most grave; while another fifth is living in constant fear of being or becoming their victims.

In fact, diseases of the lungs and heart far exceed those of any-other class in prevalence and fatality—consumption, so called, causing one fourth of the mortality between the ages of seventeen and thirty-five years—while diseases of the heart are of well-known formidable character, and raise the proportion of thoracic or pectoral diseases to a surprising ratio.

The study of this subject, as regards the causes and preventives, the symptoms and cure, has received the diligent attention of scientists and sanitarians as well as of physicians.

Leaving to the physician his subject in its multiple and exhaustless forms, I propose in this paper to give some account of the practical diagnosis, or methods of determining the nature, exact locality, and extent of thoracic disease, by means of stethoscopy, or the physical exploration of the chest.

The thorax incloses the essentially vital organs—the lungs with their pleurae, or delicate membranous coverings, and the heart with its pericardium and great blood-vessels. These, actuated through their system of nerve-filaments, give the rhythmic heavings of respiration and the throb and pulses of the blood-circulation.

Although so admirably guarded against harm by the strong and elastic chest-walls, and against all inimical approach by that ever-vigilant sentinel, the epiglottis, they are, from the very nature of their functions, preeminently subject to danger from without as well as from within. The delicate mechanism of living lung-tissue can not be subjected to direct observation; the minute cells for containing air would be crushed by air admitted from without, and the heart arrested for a moment for inspection would never beat again; yet the vital operations of these organs are well understood and their morbid conditions can be read almost as if exposed to view.

On firmly applying the ear to the walls of the chest of a person in health, certain sounds can be heard, varying in loudness and clearness with the quarter of the chest at which the ear is applied, and with the age or individual peculiarity of the person examined, or his state of action or repose. The double sound of the heart, embracing what are known as the first and second sounds, is heard distinctly: the former caused by the strong muscular contractions of the ventricles, mainly the left, whose function it is to distribute the blood to the system.