On Longevity And Shortness Of Life
The following considerations may enable us to understand the reasons
for all these facts. We must remember that an animal is by nature
humid and warm, and to live is to be of such a constitution, while old
age is dry and cold, and so is a corpse. This is plain to observation.
But the material constituting the bodies of all things consists of the
following-the hot and the cold, the dry and the moist. Hence when they
age they must become dry, and therefore the fluid in them requires
to be not easily dried up. Thus we explain why fat things are not
liable to decay. The reason is that they contain air; now air
relatively to the other elements is fire, and fire never becomes
Again the humid element in animals must not be small in quantity,
for a small quantity is easily dried up. This is why both plants and
animals that are large are, as a general rule, longer-lived than the
rest, as was said before; it is to be expected that the larger
should contain more moisture. But it is not merely this that makes
them longer lived; for the cause is twofold, to wit, the quality as
well as the quantity of the fluid. Hence the moisture must be not only
great in amount but also warm, in order to be neither easily congealed
nor easily dried up.
It is for this reason also that man lives longer than some animals
which are larger; for animals live longer though there is a deficiency
in the amount of their moisture, if the ratio of its qualitative
superiority exceeds that of its quantitative deficiency.
In some creatures the warm element is their fatty substance, which
prevents at once desiccation and congelation; but in others it assumes
a different flavour. Further, that which is designed to be not
easily destroyed should not yield waste products. Anything of such a
nature causes death either by disease or naturally, for the potency of
the waste product works adversely and destroys now the entire
constitution, now a particular member.
This is why salacious animals and those abounding in seed age