STRUCTURE OF THE LUNGS. 167 



1 m quantity and quality of the blood have a most 

 direct ,ind material influence upon the condition of 

 every part of the body. If the quantity sent to the 

 arm, for example, be diminished by tying the artery 

 through which it is conveyed, the arm, being then 

 imperfectly nourished, wastes away, and does not 

 regain its plumpness till the full supply of blood be 

 restored In like manner, when the quality of that 

 fluid is impaired by deficiency of food, bad digestion, 

 impure air, or imperfect sanguification in the lungs, 

 the body aad all its functions become more or less 

 disordered- Thus, in consumption, death takes 

 place chiefly in consequence of respiration not 

 being sufficiently perfect to admit of the formation 

 of proper blood in the lungs. 



A knowledge of the structure and functions of the 

 lungs, and of the conditions favourable to their 

 healthy action, is, therefore, very important ; for on 

 their welfare depends that of every organ of the 

 body. And when we recollect that, in the British 

 Isles alone, noarly fifty thousand persons fall vic- 

 tims annually to pulmonary consumption, and that 

 these are chiefly among the young and most gifted, 

 we cannot but feel deeply interested in obtaining 

 some acquaintance with the organization which is 

 the seat of that affection, and with the conditions 

 most conducive to the due performance of its func- 

 tions and the preservation of its health. 



The exposure of the blood to the action of the 

 air seems to be indispensable to every variety of 

 animated creatures. In man and the more perfect 

 of the lower animals it is carried on in the lungs, the 

 structure of which is admirably adapted for the pur- 

 pose. In many animals, however, the requisite ac- 

 tion is effected without the intervention of lungs. 

 In fishes, for example, which live in a dense medium, 

 and do not breathe, the blood circulates through the 

 gills, which, being constantly and directly in con- 

 tact with the water, are therefore more accessible 



