476 RESPIRATION 



position within the thoracic cavity. Posteriorly, these organs meet 

 with the resistance of the vertebral column, and above, with that of the 

 structures situated at the base of the neck. Centrally, their enlarge- 

 ment is opposed by the heart and large blood-vessels For this reason, 

 they seek in general a downward and outward course, their roots mov- 

 ing downward and forward and their anterior margins downward 

 and inward. These changes enable their borders to move closer 

 together. Their exact boundaries may be made out at any time by 

 the method of percussion which consists in holding a thin plate of 

 rubber firmly against the external surface of the chest and in sharply 

 tapping upon it with a small bolstered hammer (Piorry'spleximeter). 

 A more convenient procedure is to apply the third finger of the left 

 hand to the chest and to strike it with the bent second or third finger 

 of the right hand. The sound elicited in this way Varies with the 

 nature of the subjacent tissues. If the lung tissue underneath is fully 

 expanded, a clear resonant sound is evoked. Consolidated lung 

 tissue, on the other hand, imparts a dull character to this sound, while 

 partly infiltrated tissue gives rise to intermediate notes. The same 

 holds true if the layer of the subjacent pulmonary tissue is thin. 



Anteriorly, the apices of the lungs are situated 3-7 cm. above the 

 clavicle,* and posteriorly, at about the level of the seventh spinous 

 process. When held in the expiratory position, their lower borders 

 extends in front from the upper edge of the sixth rib obliquely down- 

 ward to the level of the tenth rib at the back of the chest. A deep 

 inspiration forces this boundary downward until it rests in front, 

 opposite the seventh rib and behind, opposite the eleventh rib. Quite 

 similarly, a forceful expiration allows their lower boundary to ascend 

 to about the next ribs above those mentioned previously. Complete 

 dulness prevails in the region of the heart, but the size of this area 

 differs with the degree of expansion of the lung. When in the expira- 

 tory position, the anterior border of the left organ remains at some dis- 

 tance from the midsternal line, thereby increasing the cardiac dulness 

 until it embraces a triangular space which is limited by the left border 

 of the sternum, the fourth costosternal articulation and the sixth costal 

 cartilage. In a robust man whose arms are held in the horizontal 

 position, the circumference of the chest at the level of the nipples 

 measures 82 cm. on expiration and 89 cm. on deep inspiration. At 

 the level of the ensiform cartilage these measurements are 76 cm. and 

 83 cm. respectively. In infants and old people, however, the cir- 

 cumference of the lower part of the thorax is usually greater; moreover, 

 the right side of the adult is prone to be larger than the left on account 

 of its greater muscular development. 



Respiratory Sounds. — If the ear is applied to the chest over per- 

 fectly sound lung tissue, a soft rustling sound is heard during inspira- 

 tion which is designated as the vesicular murmur. It is thought to 

 arise either in the alveoli or at the point where the bronchiolar ter- 

 minals open into the much larger infundibula. Obviously, its cause 



