On Youth And Old Age, On Life And Death, On Breathing   

animals. Also when dealing with respiration by means of the nostrils

he imagines he is dealing with what is the primary kind of

respiration. Even the breath which passes through the nostrils

passes through the windpipe out of the chest as well, and without

the latter the nostrils cannot act. Again, when animals are bereft

of respiration through the nostrils, no detrimental result ensues,

but, when prevented from breathing through the windpipe, they die.

Nature employs respiration through the nostrils as a secondary

function in certain animals in order to enable them to smell. But

the reason why it exists in some only is that though almost all

animals are endowed with the sense of smell, the sense-organ is not

the same in all.

A more precise account has been given about this elsewhere.

Empedocles, however, explains the passage inwards and outwards of

the breath, by the theory that there are certain blood-vessels, which,

while containing blood, are not filled by it, but have passages

leading to the outer air, the calibre of which is fine in contrast

to the size of the solid particles, but large relatively to those in

the air. Hence, since it is the nature of the blood to move upwards

and downwards, when it moves down the air rushes in and inspiration

occurs; when the blood rises, the air is forced out and the outward

motion of the breath results. He compares this process to what

occurs in a clepsydra.



Thus all things outwards breathe and in;- their flesh has tubes

Bloodless, that stretch towards the body's outmost edge,

Which, at their mouths, full many frequent channels pierce,

Cleaving the extreme nostrils through; thus, while the gore

Lies hid, for air is cut a thoroughfare most plain.

And thence, whenever shrinks away the tender blood,

Enters the blustering wind with swelling billow wild.

But when the blood leaps up, backward it breathes. As when