Licence: Public Domain Mark
Credit: The nervous system and its conservation. Source: Wellcome Collection.
Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.
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![concerned are widely separated, as the}^ run from the receptors to the central apparatus. The olfactory fillers, as we have seen before, plunge into the under surface of the cerebrum itself. The fibers on which taste depends are probably scattered in the trunks of two or three nerves, and their arrangement is thought to be subject to a good deal of individual variation, ])ut it is certain that their place of entrance into the su])stance of the brain is far back of that for the impulses from the organ of smell. Sensations.—We are now in a position to make some general statements based on the outlines of the afferent system which have been given. It is evident that chan- nels to the number of millions exist by which the central nervous system may be approached from without. The impulses moving along these pathways may have been started by changes in mechanical relations at the nerve- endings (pressure, tension, vibration). In certain cases they may be the result of temperature changes, either elevations or depressions. In other instances, including the action of the organs of taste, smell, and vision, the immediate source of the impulses must be described as a chemical change. However they may originate, the biologic function of all these inflowing currents is to determine adaptive reactions of the reflex tj^pe. But as human beings we find the sensations which are associated with the arrival of certain of these im- pulses of the greatest interest. Either intensity or novelty of stimulation will be likely to insure an echo in conscious- ness. We are usually quite ignorant of the state of most of our internal organs; this does not mean that no im- pulses are ascending from them to the brain, but rather that these impulses have a monotonous character. Foster is responsible for the assertion that we should instantly miss the sensory contribution of the viscera if it should cease. To put the proposition somewhat crudely, we may say that we have no sensations from the alimentary canal, but we should, in all probability, realize a difference if it](https://iiif.wellcomecollection.org/image/b21206545_0086.jp2/full/800%2C/0/default.jpg)
