84 DISEASES OF THE LUNGS. 



horse, it is not likely to be forgotten : by exertion it may be rendered 

 still more characteristic. In a state of health even, it will be found to 

 vary with age, condition, temperament, and breeding. In the young it 

 is strongest. In human practice, its intense sound in infants is de- 

 signated puerile respiration. Leblanc proposes in young animals to call 

 it juvenile. In the aged it is hardly perceptible. The disposition of the 

 pulmonary air-cells in the young, adult, and old animals, as shown by 

 Majendie, admits of satisfactory explication of these modifications. If 

 in young animals the air-cells be more numerous and smaller, the sound 

 ought to be stronger, from the air entering into more places and through 

 more circuitous routes. If, on the contrary, as in the old, the air-cells be 

 larger and less numerous, there must be less dilatation, and more free 

 passage of air, and consequently less sound. Laennec's explanation is 

 different from this. He supposes the air-cells not to be capable of equal 

 expansion in the adult animal, in consequence of their sides becoming 

 hard. The feeble murmur heard in pulmonary emphysema, wherein the 

 air-cells are dilated or distended, favours our view of the question. In 

 fat animals, cart-horses especially, and such as are of a lymphatic 

 temperament, whose chests are covered with thick skins and abundance of 

 cellular tissue, the respiratory murmur is scarcely perceptible. In these 

 cases, one must have recourse to exertion. Drs, Chomel and Beau, the 

 last in particular, have a notion, that the murmur is produced by the 

 reflection of the shock the column of air receives against the fauces or 

 glottis, back into the ramifications of the bronchi. But how can such a 

 theory explain the supplementary murmur in one lung when the other is 

 hepatized, unless it be by a sound more vesicular — stronger — in the 

 healthy lung ; and in the superior part of the lung when the inferior is 

 no longer permeable to air. Besides, if tracheotomy be performed, and 

 afterwards the nostrils sewn up, the murmur is still heard, although the 

 animal is respiring through an aperture below the place where, according 

 to M. Beau, the collision happens which produces the sound in question. 

 The respiratory murmur will be found to vary according to the region of 

 the chest auscultated. In the middle region it is heard distinctly behind 

 the shoulder, increasing a little thence to the ninth rib, afterwards 

 gradually decreasing to the last. Along the superior region the sound is 

 quite distinct, as well as below and behind the cartilage of the scapula — 

 behind a mass of fat lodged there in fat subjects. At this place we have 

 invariably found the murmur louder than elsewhere, and we ascribe this 

 to the passage of the air through the larger divisions of the bronchi, 

 they being situated hereabouts : to it we give the name of bronchial 

 respiration; thus making a distinction between it and the murmur. Along 

 the inferior region the respiratory murmur again becomes distinct enough 

 from behind the elbow to the ninth rib; whence it diminishes to the 

 seventeenth, and U there lost. The sound is the same on both sides, 



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