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a slow, progressive contraction of the muscular coat of the intestines is established, which continues for some time after the irritation is removed. Division of the sympathetic nerve in the neck is followed by a vascular congestion of the parts above the section on the corresponding side, attended by an increase in the temperature; not only is there an increase in the amount of blood, but the rapidity of the blood current is very much hastened and the blood in the veins becomes of a brighter color. Galvanization of the upper end of the divided nerve causes all of the preceding phenomena to disappear; the congestion decreases, the temperature falls, and the venous blood becomes dark again.

The sympathetic exerts a similar influence upon the circulation of the limbs and the glandular organs; destruction of the first thoracic ganglion and division of the nerves forming the lumbar and sacral plexuses is followed by a dilatation of the vessels, an increased rapidity of the circulation, and an elevation of temperature in the anterior and posterior limbs ; galvanization of the peripheral ends of these nerves causes all of these phenomena to disappear. Division of the splanchnic nerve causes a dilatation of the blood vessels of the intestine.

These phenomena of the sympathetic nerve system are dependent upon the presence of vasomotor nerves, which, under normal circumstances, exert a tonic influence upon the blood-vessels. These nerves, derived from the cerebro-spinal system, the medulla oblongata, leave the spinal cord by the rami communicantes, enter the sympathetic ganglia, and finally terminate in the muscular wall of the blood-vessels.

Sleep is a periodical condition of the nervous system, in which there is a partial or complete cessation of the activities of the higher nerve centers. The cause of sleep is a diminution in the quantity of blood, occasioned by a contraction of the smaller arteries under the influence of the vasomotor

nerves.

During the waking state the brain undergoes a physiological waste, as a result of the exercise of its functions; after a certain length of time its activities become enfeebled, and a period of repose ensues, during which a regeneration of its substance takes place.

When the brain becomes enfeebled there is a diminished molecular activity and an accumulation of waste products ; under these circumstances it ceases to dominate the medulla oblongata and the spinal cord. These centers then act more vigorously, and diminish the caliber of the cerebral blood-vessels through the action of the vasomotor nerves, producing a condition of physiological anemia and sleep; during this state waste products are removed, force is stored up, nutrition is restored, and waking finally THE SENSE OF TOUCH. The Sense of Touch is a modification of general sensibility, and located in the skin, which is especially adapted for this purpose, on account of the number of nerves and papillary elevations it possesses. The structures of the skin and the modes of termination of the sensory nerves have already been considered.

occurs.

The Tactile Sensibility varies in acuteness in different portions of the body, being most marked in those regions in which the tactile corpuscles are most abundant, e.g., the palmar surface of the third phalanges of the fingers and thumb.

The relative sensibility of different portions of the body has been ascertained by means of a pair of compasses, the points of which are guarded by cork, and then determining how closely they could be brought together, and yet be felt at two distinct points. The following are some of the measure

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The sense of touch communicates to the mind the idea of resistance only, and the varying degrees of resistance offered to the sensory nerves enable us to estimate, with the aid of the muscular sense, the qualities of hardness and softness of external objects. The idea of space or extension is obtained when the sensory surface or the external object changes its place in regard to the other; the character of the surface, its roughness or smoothness, is estimated by the impressions made upon the tactile papillæ.

Appreciation of Temperature. The general surface of the body is more or less sensitive to differences of temperature, though this sensation is separate from that of touch; whether there are nerves especially adapted for the conduction of this sensation has not been fully determined. Under pathological conditions, however, the sense of touch may be abolished, while the appreciation of changes in temperature may remain normal.

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