require rapid refrigeration because there is little scope for

deviation from the normal amount of their vital fire; the air also

must penetrate all through it on account of the large quantity of

blood and heat it contains. But both these operations can be easily

performed by air, for, being of a subtle nature, it penetrates

everywhere and that rapidly, and so performs its cooling function; but

water has the opposite characteristics.

The reason why animals with a full-blooded lung respire most is

hence manifest; the more heat there is, the greater is the need for

refrigeration, and at the same time breath can easily pass to the

source of heat in the heart.



22



In order to understand the way in which the heart is connected

with the lung by means of passages, we must consult both dissections

and the account in the History of Animals. The universal cause of

the need which the animal has for refrigeration, is the union of the

soul with fire that takes place in the heart. Respiration is the means

of effecting refrigeration, of which those animals make use that

possess a lung as well as a heart. But when they, as for example the

fishes, which on account of their aquatic nature have no lung, possess

the latter organ without the former, the cooling is effected through

the gills by means of water. For ocular evidence as to how the heart

is situated relatively to the gills we must employ dissections, and

for precise details we must refer to Natural History. As a summarizing

statement, however, and for present purposes, the following is the

account of the matter.

It might appear that the heart has not the same position in

terrestrial animals and fishes, but the position really is

identical, for the apex of the heart is in the direction in which they

incline their heads. But it is towards the mouth in fishes that the