In ordinary quiet breathing, the air simply flows along the lower nasal passages into the pharynx, scarcely entering the olfactory chamber at all. This is the reason why, when we wish to perceive a faint odor, we sniff up the air sharply. By so doing, the air which is forcibly drawn into the nostrils passes up even into the higher olfactory chamber, where some of the floating particles of the odorous material come into contact with the nerves of smell. One of the most essential conditions of the sense of smell is that the nasal passages be kept well bathed in the fluid secreted by the lining membrane. At the beginning of a cold in the head, this membrane becomes dry and swollen, thus preventing the entrance of air into the upper chamber, deadening the sensibility of the nerves, and thus the sense of smell is greatly diminished. The delicacy of the sense of smell varies greatly in different individuals and in different animals. It is generally more acute in savage races. It is highly developed in both the carnivora and the herbivora. Many animals are more highly endowed with this sense than is man. The dog, for example, appears to depend on the sense of smell almost as much as on sight. It is well known, also, that fishes have a sense of smell. Fragments of bait thrown into the water soon attract them to a fishing ground, and at depths which little or no light can penetrate. Deer, wild horses, and antelopes probably surpass all other animals in having a vivid sense of smell. Smell has been defined as “taste at a distance,” and it is obvious that these two senses not only form a natural group, but are clearly associated in their physical action, especially in connection with the perception of the flavor of food. The sense of odor gives us information as to the quality of food and drink, and more especially as to the quality of the air we breathe. Taste is at the gateway of the alimentary canal, while smell acts as the sentinel of the respiratory tract. Just as taste and flavor influence nutrition by affecting the digestive process, so the agreeable odors about us, even those of the perfumes, play an important part in the economy of life. 324. The Sense of Sight. The sight is well regarded as the highest and the most perfect of all our senses. It plays so common and so beneficent a part in the animal economy that we scarcely appreciate this marvelous gift. Sight is essential not only to the simplest matters of daily comfort and necessity, but is also of prime importance in the culture of the mind and in the higher forms of pleasure. It opens to us the widest and the most varied range of observation and enjoyment. The pleasures and advantages it affords, directly and indirectly, have neither cessation nor bounds.