Theophr. _de sens._ 27; _Dox._ 507. Anaxagoras held that sensation takes place by opposite qualities; for like is not affected by like. And he attempts to enumerate things one by one. For seeing is a reflection in the pupil, and objects are not reflected in the like, but in the opposite. And for many creatures there is a difference of colour in the daytime, and for others at night, so that at that time they are sharpsighted. But in general the night is more of the same colour as the eyes. And the reflection takes place in the daytime, since light is the cause of reflection; but that colour which prevails the more is reflected in its opposite. In the same manner both touch and taste discern; for what is equally warm or equally cold does not produce warm or cold when it approaches its like, nor yet do men recognise sweet or bitter by these qualities in themselves, but they perceive the cold by the warm, the drinkable water by the salt, the sweet by the bitter, according as each quality is absent; for all things are existing in us. So also smell and hearing take place, the one in connection with breathing, the other by the penetration of sound into the brain; for the surrounding bone against which the sound strikes is hollow. And every sensation is attended with pain, which would seem to follow from the fundamental thesis; for every unlike thing by touching produces distress. And this is evident both in the duration and in the excessive intensity of the sensations. For both bright colours and very loud sounds occasion pain, and men are not able to bear them for any long time. And the larger animals have the more acute sensations, for sensation is simply a matter of size. For animals that have large, pure, and bright eyes see large things afar off, but of those that have small eyes the opposite is true. And the same holds true of hearing. For large ears hear large sounds afar off, smaller ones escape their notice, and small ears hear small sounds near at hand. And the same is true of smell; for the thin air has the stronger odour, since warm and rarefied air has an odour. And when a large animal breathes, it draws in the thick with the rarefied, but the small animal only the rarefied, so that large animals have a better sense of smell. For an odour near at hand is stronger than one far off, because that is thicker, and what is scattered is weakened. It comes about to this, large animals do not perceive the thin air, and small animals do not perceive the thick air.