Page:Popular Science Monthly Volume 81.djvu/173

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have the capacity of picking up sound waves of a much higher pitch than those which impress our duller senses, while the greater acuity of vision of birds, the keener sense of smell of various animals, the delicacy of perception of fishes for changes in pressure, are facts that are too well known to need repetition. To a certain extent these great differences in sense perception are directly referable to peculiarities in structure. The same fundamental system of construction characterizes the nervous system of the entire animal kingdom. The structural unit is the nerve-cell and nerve-fiber. The greater the number of these cells and fibers the greater is the complexity of the nervous system. Some of the cells are designed to pick up and transfer to the distributing apparatus the stimuli for which the organs are attuned. In addition to the receiving apparatus there is the transformer and elaborator of the incoming impulses, and finally there is the discharging apparatus as represented by the organs of locomotion, speech and. others, which express objectively the sum total of the animal's activities. Already science has taught us something about the nature of that mysterious nervous impulse upon which thought, action and life depend. In fact there is a similarity between the rhythmic character of the life processes and the rhythmic discharges of certain types of cells in a battery. Here, as in all other enquiries which concern the energies of living matter, we are led back to the study of the cell. The millions of cells composing our bodies have certain common characteristics. The central portions are probably the parts most immediately related to the production of energy, while the external layers govern the taking in or throwing off of substances by the cell. A theory in regard to the manner in which anesthetics act attributes an important role to this external layer, as the place where.the actual physico-chemical changes take place that result in anesthesia. The effects depend to a certain extent upon the presence in this outer envelope of certain fat-like substances which, combining with the enhaled ether or chloroform, produce loss of consciousness. There are also reasons for believing that in this same external layer of the cell the nerve impulse is generated, depending upon changes akin in their manifestation and mode of origin to those giving rise to electrical disturbances. One of the greatest services yet rendered biology by physical chemistry is the presentation of the facts suggesting that the regulation of the production of nerve impulses is not dependent upon some vague mysterious vital force, but is probably comparable to those phenomena called by the chemists "reversible reactions." The mixture of two substances may be followed by a chemical reaction in which the two original substances are in part decomposed, forming new chemical compounds. At a certain point this reaction ceases, as an equilibrium has been established, and then only after the balance has again been disturbed is the decomposition completed or a