316 RESPIRATORY APPARATUS. 



as they are lodged beneath the hypochondrium. Below, the sound is 

 dull, on account of the gastric comj^artments generally being full of 

 food. 



Certain trifling modifications of this normal condition may be noted, 

 depending on the degree of fatness or thinness of the subjects. The 

 j)athological changes which may occur are as follows : — 



A tympanic sound, with or without metallic character, may be found 

 at a point where normally one would expect a clear sound (pneumo- 

 thorax, diaphragmatic hernia). A dull sound may be met with in the 

 same regions, all resonance being lost (pneumonia, broncho-pneumonia, 

 pleural exudate, etc.). Partial dulness and partial loss of resonance may 

 occur in regions which ought to give a resonant sound (deep pneumonia, 

 tuberculous lesions, the presence of echinococcus cysts, etc.). 



Auscultation — i.e., examination by means of the ear — is the most 

 valuable method of discovering and localising pulmonary, pleural, or 

 cardiac lesions. 



Various sensations are conveyed to the ear, depending on the method 

 in which the normal or pathological sounds are produced. 



The deductions to be drawn as regards the nature of existing disease 

 are based on the intensity, character, duration, and special attributes of 

 the sounds noted. 



Direct auscultation is the most certain method, but the ear cannot be 

 a]3plied with equal facility at all points. Under such circumstances 

 a simple or binaural stethoscope, or the phonendoscope, may be used 

 with advantage. 



To properly appreciate the sounds heard it is essential to be exactly 

 acquainted with the relation between the lung and thorax. On the left 

 side (Fig. 60) the anterior pulmonary lobe occupies the space between 

 the first and fourth ribs, in front and above the base of the heart. The 

 middle, or cardiac, lobe covers the left upper and postero-lateral part 

 of the heart from the fourth to the sixth rib. The posterior lobe 

 occupies all the region beyond the sixth rib as far as the twelfth. 



On the right side the arrangement is similar, but the anterior lobe 

 and the cardiac lobe are more developed (Fig. 62). 



Under ordinary circuinstances the extensive movement of the lung 

 which occurs during inspiration produces a special sound known as the 

 respiratory or vesicular murmur. Contrary to what has been written 

 and said, this sound in animals possessing absolutely sound lungs ends 

 with inspiration. Expiration is silent, though it is easy to estimate 

 its duration. 



In auscultating the lung, we may distinguish four zones, a superior 

 zone, a middle zone, an inferior zone, and a scapular zone. 



The superior zone is bounded by the vertebro-costal gutter, descends. 



