of phenomena which occur in these organs. The
term _sanguification_ is occasionally used to denote that part of the
process in which the blood, by exposure to the action of the air, passes
from the venous to the arterial state. As the chyle does not become
assimilated to the blood until it has passed through the lungs, this
term, which signifies _blood-making_, is not unaptly used.

The _quantity_ and _quality_ of the blood have a most direct and
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 and 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 favorable to
_their_ healthy action, is therefore very important, for on their
welfare depends that of every organ of the body.

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 purpose. In many
animals, however, the requisite action is effected without the
intervention of lungs. In fishes, for example, that live in water and do
not breathe, the blood circulates through the gills, and in them is
exposed to the air which the water contains. So necessary is the
atmospheric air to the vitality of the blood in all animals, that the
want of it inevitably proves fatal. A fish can no more live in water
deprived of air, than a man could in an atmosphere devoid of oxygen,
which is the element that unites with the blood in the lungs in
sanguification.

In man the lungs are those large, light, spongy bodies which, along with
the heart, completely fill up the cavity of the chest. They vary much in
size in different persons; and as the chest is formed for their
protection, it is either large and capacious, or the reverse, according
to