Theophrastus, in commenting upon the doctrine of Empedokles, takes as one of his grounds of objection--That Empedokles, in maintaining sensation and knowledge to be produced by influx of the elements into pores, made no difference between animated and inanimate substances (Theophr. De Sens. s. 12-23). Theophrastus puts this as if it were an inconsistency or oversight of Empedokles: but it cannot be so considered, for Empedokles (as well as Parmenides) appears to have accepted the consequence, and to have denied all such difference, except one of degree, as to perception and knowledge.] [Footnote 131: Emp. Frag. 316, Karst. [Greek: ai(=ma ga\r a)nthrô/pois perika/rdio/n e)sti no/êma.] Comp. Theophrast. De Sensu, s. 11.] [Side-note: Sense of vision.] In regard to vision, Empedokles supposed that it was operated mainly by the fire or light within the eye, though aided by the light without. The interior of the eye was of fire and water, the exterior coat was a thin layer of earth and air. Colours were brought to the eye as effluvia from objects, and became apprehended as sensations by passing into the alternate pores or ducts of fire and water: white colour was fitted to (or in symmetry with) the pores of fire, black colour with those of water.[132] Some animals had the proportions of fire and water in their eyes better adjusted, or more conveniently located, than others: in some, the fire was in excess, or too much on the outside, so as to obstruct the pores or ducts of water: in others, water was in excess, and fire in defect. The latter were the animals which saw better by day than by night, a great force of external light being required to help out the deficiency of light within: the former class of animals saw better by night, because, when there was little light without, the watery ducts were less completely obstructed--or left more free to receive the influx of black colour suited to them.[133] [Footnote 132: Emp. Frag. v. 301-310, Karst. [Greek: to/ t' e)n mê/nigxin e)ergme/non ô)gu/gion pu=r], &c. Theophr. De Sensu, s. 7, 8; Aristot. De Sensu, c. 3; Aristot. De Gen. et Corrupt. i. 8.] [Footnote 133: Theophrastus, De Sensu, s. 7, 8.] [Side-note: Senses of hearing, smell, taste.]