168 STRUCTURE OF THE LUNGS. 



to the action of the air which the water contains, 

 and much better adapted than lungs would be to 

 the medium in which fishes live. In worms, on 

 the other hand, and many similar animals, no dis- 

 tinct organ is set apart for the purpose, but the 

 aeration of the blood takes place at the surface of 

 the body by means of pores in the skin called spira* 

 cula, specially adapted to this end, and which cannot 

 be shut up or obstructed any more than the real 

 lungs or gills without inducing death. So neces- 

 sary, indeed, is atmospheric air to the vitality of the 

 blood in all classes of animals, that its abstraction 

 inevitably induces death ; and a fish can no more 

 live in water deprived of air than a man could do in 

 an atmosphere devoid of oxygen. And thus the 

 fish requires a renewal of air, and perishes when it 

 is denied, exactly as man does in similar circum- 

 stances. 



In man, the lungs are those large, light, spongy 

 bodies which, along with the heart, completely fill 

 the two lateral cavities of the chest. They vary 

 much in size in different persons, and, as the chest 

 is formed for their protection, we find it either large 

 and capacious, or the reverse, according to the size 

 which the lungs have attained. Their position re- 

 latively to the other viscera may be understood on 

 reference to the subjoined woodcut, which repre- 

 sents the various organs of the chest and belly as 

 they appear on removing the integuments, breast- 

 bone, and part of the ribs. The sketch is rather 

 rude, but it will serve the purpose. The letters R L 

 and L L mark the right and left lungs, with H the 

 heart lying between them, but chiefly on the left 

 side. V is an inaccurate representation of the 

 large blood-vessels going to the head, neck, and 

 superior extremities. Liv r is the liver, lying in 

 the abdomen or belly, and separated from the 

 chest by the arched fleshy partition D D, called 

 the diaphragm or midriff. The stomach appears on 



