On Sense And The Sensible   

For his brain is naturally cold, and the blood which it contains in

its vessels is thin and pure but easily cooled (whence it happens that

the exhalation arising from food, being cooled by the coldness of this

region, produces unhealthy rheums); therefore it is that odours of

such a species have been generated for human beings, as a safeguard to

health. This is their sole function, and that they perform it is

evident. For food, whether dry or moist, though sweet to taste, is

often unwholesome; whereas the odour arising from what is fragrant,

that odour which is pleasant in its own right, is, so to say, always

beneficial to persons in any state of bodily health whatever.

For this reason, too, the perception of odour [in general]

effected through respiration, not in all animals, but in man and

certain other sanguineous animals, e.g. quadrupeds, and all that

participate freely in the natural substance air; because when

odours, on account of the lightness of the heat in them, mount to

the brain, the health of this region is thereby promoted. For odour,

as a power, is naturally heat-giving. Thus Nature has employed

respiration for two purposes: primarily for the relief thereby brought

to the thorax, secondarily for the inhalation of odour. For while an

animal is inhaling,- odour moves in through its nostrils, as it were

'from a side-entrance.'

But the perception of the second class of odours above described

[does not belong to all animal, but] is confined to human beings,

because man's brain is, in proportion to his whole bulk, larger and

moister than the brain of any other animal. This is the reason of

the further fact that man alone, so to speak, among animals

perceives and takes pleasure in the odours of flowers and such things.

For the heat and stimulation set up by these odours are commensurate

with the excess of moisture and coldness in his cerebral region. On

all the other animals which have lungs, Nature has bestowed their

due perception of one of the two kinds of odour [i.e. that connected

with nutrition] through the act of respiration, guarding against the