soluble in water, but, on the other hand, retards the diffusion of odorous vapors. The temperature of the laboratory in which smell experiments are in progress should be kept as uniform as possible, and thermometer and barometer readings should be taken whenever the stimulus-limen is determined. Uniformity of temperature was not secured in our own experiments.
II. The Rate of Diffusion of Odorous Vapor. Cloquet pointed out in 1821 that odors diffuse in the air as one gas diffuses in another,—gradually, and without interruption by reflection or refraction,—so that if the air is at rest, the strength of a smell will be inversely proportional to the distance of its source, though the speed with which different odors travel varies much.[1] Now the air from which we draw our breath is, under ordinary circumstances, almost never free from currents. For phylogenetic reasons, no gas is odorous which is not heavy enough to remain near its source if undisturbed. Yet the wind may carry such gases for miles near the surface of the ground. Nor can we, in view of the dynamic theory of smell, and of Liegois's theory that odorous particles are largely diffused in the form of tiny liquid drops which afterwards vaporize, unhesitatingly apply the laws of diffusion of gases to smells. Zwaardemaker has, however, proved by a series of experiments that the transmission of odorous vapors in tubes takes place at the same rate for different distances from the source, unless these distances are very considerable.[2] From an inhaling-tube, all currents of air, except the suction-current created by the inspiration, are excluded.
III. The Rate and Manner of Breathing. Not all the air which passes through the noise comes in contact with the olfactory mucous membrane. The current of air drawn into the nose from without is divided by the lower turbinal bone into two portions. From the stream which takes the direct path to the choana under this bone and along the floor of the nose, no odorous vapor reaches the olfactory membrane. Each nasal cavity is divided by the middle turbinal bone into two chambers. In the upper chamber, which extends from the pointed roof of the nose to the under edge of the middle turbinal bone, the side wall and the septum are almost parallel, and only about two millimeters apart. The olfactory membrane is spread over the upper surface of these parallel walls, forming the regio olfactoria of Todd and Bowman. According to von Brunn only the uppermost part of the upper turbinal bone and the surface of the septum just opposite are covered by the ol-
