2OO Examination of CJiest 



cussing the back, the patient should, if possible, sit up in bed, fold his 

 arms across the thighs, and bend forwards. 



A strange, chinking, crack-pot sound may sometimes be heard on 

 percussing over a pulmonary cavity ; it is due to some of the air being 

 driven with each stroke into the opening of a bronchial tube. This 

 may be imitated by keeping the palms of the hands loosely closed 

 across each other, and then striking the back of one hand on the knee. 

 If the hollow between the hands be made air-tight, the crack-pot sound 

 is lost ; similarly the pulmonary cavity must have a clear bronchial 

 tube opening out of it, or it becomes an air-tight chamber and the sound 

 is lost. 



Vocal fremitus is the thrill of the vibrating vocal cords which is 

 conveyed by the air in trachea, bronchi, and vesicles to the hands placed 

 upon the chest. The nearer to the larynx, the larger the bronchus and 

 the louder the fremitus. It is * damped ' by a thick layer of fat or 

 muscle upon the chest, and by air in the pleura ; whilst it is completely 

 drowned by pleuritic effusion (p. 189). Its absence from the back of the 

 lung, therefore, is a diagnostic sign between pleurisy with slight effusion 

 and pneumonia ; in the latter the vibrations are absolutely increased, 

 for the solid lung is a good conductor of sound. Returning fremitus 

 denotes absorption of fluid. 



On listening at one end of a wooden beam whilst someone scratches 

 the other end with a pin, the scratches are heard with extraordinary 

 distinctness, for the solid material not only conveys the vibrations, but 

 magnifies them. Similarly in exudation into the lung the vopal fremi- 

 tus is exaggerated, provided always that the bronchial tubes are free 

 to convey the vibrations from the trachea to the lung-tissue. 



A pulmonary cavity may act as a reservoir, or a sounding-board for 

 vocal vibrations (provided that it is not full of fluid), and thus vocal 

 fremitus may be increased, especially if the surrounding lung-tissue 

 be solid. 



The healthy respiratory sounds vary with the site in which auscul- 

 tation is made. Thus, if the stethoscope be placed over the episternal 

 region, or over the spines of the lower cervical or upper dorsal verte- 

 bras, and the patient draw a deep breath, the air is heard rushing 

 through the trachea this is tracheal respiration. It is a good deal 

 like the blow of air through a keyhole. If the stethoscope be placed 

 between the scapulas, or over the. sternum, the tidal blow is heard in a 

 less degree, termed bronchial, or tubular. In other parts of the chest 

 than over the trachea or bronchi the respiratory, or vesicular mur- 

 mur, or breath-sound is heard as a soft blow, which has been poetically 

 likened by Hughes to * the song of a gentle gale in the thick summer 

 foliage, or to the whisper of the retiring wave upon a sandy coast.' 



When the pleura is full of air or liquid, and the lung lies collapsed 

 against the spine, air still enters and leaves the larger bronchi, and 

 so bronchial respiration is present in pneumothorax and empyema as 



