. The physiology of domestic animals ... Physiology, Comparative; Veterinary physiology. 846 PHYSIOLOGY OP THE DOMESTIC ANIMALS. The intensity of the sense of smell depends, first, upon the size of the olfactory surface, since we iind that in animals in which the sense of smell is most acute the turbinated bones of the olfactory region are most complicated ; secondly, on the concentration of the odorous sub- stance in the air; and, thirdly, on the frequency with which the columns of air containing the odorous particles are conducted to the olfactory organs; hence sniffing tends to increase the
. The physiology of domestic animals ... Physiology, Comparative; Veterinary physiology. 846 PHYSIOLOGY OP THE DOMESTIC ANIMALS. The intensity of the sense of smell depends, first, upon the size of the olfactory surface, since we iind that in animals in which the sense of smell is most acute the turbinated bones of the olfactory region are most complicated ; secondly, on the concentration of the odorous sub- stance in the air; and, thirdly, on the frequency with which the columns of air containing the odorous particles are conducted to the olfactory organs; hence sniffing tends to increase the intensity of odors. The development of the sense of smell is always more highly marked in animals than in man and plays an important part in their organization. Game-dogs, as is well known, will recognize the odor from game-birds at several hundred yards, but even this falls below the acuteness of smell possessed by various animals which are able to scent the presence of man at a distance of a mile or more. B. THE SENSE OF SIGHT. Vision is the perception of the sensation caused by the impression of a ray of light upon the retina, and in all animals depends upon the special sensitiveness of the optic nerve-filaments to the vibration of luminous rays. Animals may, nevertheless, be sensible of light without special organs of vision, and may even be capable of giving evidence of the impression of such light; thus, the hydra, although it has no distinct organs of vision, will move around from side to side of the vessel in which it is placed until it has reached that on which the sun is shining and will turn itself toward the seat of light. In its simplest form the visual apparatus is represented b}r a col- lection of pigment-cells in the outer coverings of the body which are in connection with the ter- mination of afferent nerves. The pigment absorbs the rays of light, and in that function some process, probabl}- of a chemical nature, is excited and the sensitive nerves are stimula
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