Aristotle On Youth and Old Age,On Life and Death,On Breathing-Part 26

In connexion with the heart there are three phenomena, which, thoughapparently of the same nature, are really not so, namelypalpitation, pulsation, and respiration.Palpitation is the rushing together of the hot substance in theheart owing to the chilling influence of residual or waste products.It occurs, for example, in the ailment known as 'spasms' and inother diseases. It occurs also in fear, for when one is afraid theupper parts become cold, and the hot substance, fleeing away, by itsconcentration in the heart produces palpitation. It is crushed into sosmall a space that sometimes life is extinguished, and the animals dieof the fright and morbid disturbance.The beating of the heart, which, as can be seen, goes oncontinuously, is similar to the throbbing of an abscess. That,however, is accompanied by pain, because the change produced in theblood is unnatural, and it goes on until the matter formed byconcoction is discharged. There is a similarity between thisphenomenon and that of boiling; for boiling is due to thevolatilization of fluid by heat and the expansion consequent onincrease of bulk. But in an abscess, if there is no evaporationthrough the walls, the process terminates in suppuration due to thethickening of the liquid, while in boiling it ends in the escape ofthe fluid out of the containing vessel.In the heart the beating is produced by the heat expanding thefluid, of which the food furnishes a constant supply. It occurs whenthe fluid rises to the outer wall of the heart, and it goes oncontinuously; for there is a constant flow of the fluid that goes toconstitute the blood, it being in the heart that the blood receivesits primary elaboration. That this is so we can perceive in theinitial stages of generation, for the heart can be seen to containblood before the veins become distinct. This explains why pulsation inyouth exceeds that in older people, for in the young the formationof vapour is more abundant.All the veins pulse, and do so simultaneously with each other, owingto their connexion with the heart. The heart always beats, and hencethey also beat continuously and simultaneously with each other andwith it.Palpitation, then, is the recoil of the heart against thecompression due to cold; and pulsation is the volatilization of theheated fluid.