A man can live without food for a few days, but without air

he cannot live even for five minutes. The moment he is born

he begins to breathe will continue to breath till he is

alive. During the process of breathing he draws some are

into his body and expels some. If this supply if air is cut

off, he is suffocated and dies.

The air we breathe in is taken

into the lungs through the wind pipe. The lunge are situated

in the chest-one in each side of the body. The air we breath

in contains oxygen to the extent of one-fifth of the volume

of air. The oxygen is dissolved in the blood and is carried

to all parts of the body. The oxygen combines with the

tissues and sets free the energy contained in them. The

combination of oxygen with a substance is known as the

process of oxidation, combustion or burning is going on in

the human body every moment of the life of a man-whether he

is awake or asleep. Heat is, of course, generated, but there

is no fire.

The whole system of

respiration can be summarized as follows :

(1) Pure blood received from the lungs is pumped by the

heart into the large arteries.

(2) Veins bring impure blood from various parts of the body

and pour it into the heart.

(3) The heart pumps it out into the lungs for purification.

Thus a cycle is formed and the process is automatic. Lungs

are the most important part of this system, because it is

they that purify the impure blood and discharge waste

products like carbon dioxide. The other parts of the

respiratory system are :

(a) the nose.

(b) The upper part of the wind-pipe which is modified into

the voice box known as larynx.

(c) The wind-pipe.

(d) The lungs.