Page:Popular Science Monthly Volume 6.djvu/154

142 the characters of the footprints belonging to each pace; the transition from one pace to another; the modification of the movements incident to pulling a load, etc., we are unable to notice here, and would therefore refer the interested reader to M. Marey's work, where he will find the subject fully elucidated.



ESCARTES, Leibnitz, and all the great minds of the seventeenth century, believed that phenomena are such interdependent parts of one whole, that they require to be explained by each other, and consequently, that a very close mutual connection should be maintained among the sciences. In their view, this was the condition of rapid advance and intelligent development. The experimental method, constant to systematic obstinacy in erecting so many barriers between the different sections of natural philosophy, has greatly hindered the completeness of whatever knowledge we possess as the result of mutual interaction among all truths. At this day, such barriers are tending to vanish of their own accord, and the science of man in his relations with external media begins to show the outlines of its plan and harmony. We have before this sketched several of its chapters, and we will endeavor now to write another, on the subject of odors.

The seat of smell, or the olfactory sense, is the pituitary membrane lining the inner wall of the nostrils. It is a mucous surface, laid in irregular wrinkles, and receiving the spreading, slender, terminal filaments of a certain number of nerves. This membrane, like all other mucous ones, constantly secretes a fluid designed to lubricate it. By the aid of the muscles covering the lower part of the nostrils, the apparatus of smelling can be dilated or contracted, precisely like that of sight. This understood, the mechanism of olfaction is quite simple. It consists in the contact of odorous particles with the olfactory nerve. These particles are conveyed by the air to the inside of the nasal cavities, and there strike upon the sensitive fibres. If the access of air is prevented, or if the nerve is altered, no sensation is produced. Experiments in physiology, in fact, have settled that the olfactory nerves (or those of the first pair) are assigned exclusively to the perception of odors. Loss of the sense of smell occurs whenever the nerves are destroyed or injured by any process, or even whenever they are merely compressed. On the other hand, it is a matter of common observation 