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

of vapour is more abundant.

All the veins pulse, and do so simultaneously with each other, owing

to their connexion with the heart. The heart always beats, and hence

they also beat continuously and simultaneously with each other and

with it.

Palpitation, then, is the recoil of the heart against the

compression due to cold; and pulsation is the volatilization of the

heated fluid.



27



Respiration takes place when the hot substance which is the seat

of the nutritive principle increases. For it, like the rest of the

body, requires nutrition, and more so than the members, for it is

through it that they are nourished. But when it increases it

necessarily causes the organ to rise. This organ we must to be

constructed like the bellows in a smithy, for both heart and lungs

conform pretty well to this shape. Such a structure must be double,

for the nutritive principle must be situated in the centre of the

natural force.

Thus on increase of bulk expansion results, which necessarily causes

the surrounding parts to rise. Now this can be seen to occur when

people respire; they raise their chest because the motive principle of

the organ described resident within the chest causes an identical

expansion of this organ. When it dilates the outer air must rush in as

into a bellows, and, being cold, by its chilling influence reduces

by extinction the excess of the fire. But, as the increase of bulk

causes the organ to dilate, so diminution causes contraction, and when

it collapses the air which entered must pass out again. When it enters

the air is cold, but on issuing it is warm owing to its contact with

the heat resident in this organ, and this is specially the case in

those animals that possess a full-blooded lung. The numerous