that his replies may depend upon his receiving information through the tested source alone, the eyes should be bandaged or other suitable precautions taken to prevent their use. Check tests must also be used, such as asking "what is felt" when nothing is applied, or by using some indifferent object in place of the one which the patient is expecting, as the finger-tip, requiring him at the same time to tell what it is.

The attending conditions must be usual and natural. It is useless to test the sensibility of chilled extremities or to expect reliable replies from the stuporous. In many instances, moreover, there is much sensory disturbance without the patient being aware of it, as in hysteria; or there may be dissolution of the various qualities of the sense of touch that has not specially attracted his attention, as in syringomyelia.

The tactile sense enables us to recognize the contact of objects with the skin. In a crude way its delicacy may be tested by stroking with a feather or flake of cotton, by touching lightly the ends of hairs growing on the limbs, or by ruder contacts when the sense is found blunted. An instrument called an esthesiometer, consisting of two movable points, is frequently employed in testing this element of the sense of touch. A pair of compasses answers the purpose. Observations are made as to the least distances at which two blunted points are both recognized when brought into contact with the skin at the same time, and in a line parallel to the course of the nerve supplied to the part. These distances vary widely, as between the tip of the tongue or finger and the dorsum of the body. The following average measurements will serve as a standard of comparison, or if the sensory disturbance be limited to one side of the body, the opposite corresponding area will furnish a better guide. Differences, to be significant, must be about double those here indicated:

TABLE SHOWING ORDINARY DISTANCES AT WHICH TWO POINTS ARE
RECOGNIZED.

Another means of testing the tactile sense is to place variouslyshaped objects on the skin and to ask a description of them, or to trace letters and numerals with a blunt point.

The pain sense may be readily investigated by using a pricking point, but it must not be too fine. A pointed quill or toothpick answers well except in marked analgesia. The patient is required to state whether a touch or a painful prick is recognized.

The pressure sense, which is not of great importance, is tested by placing on the skin objects of the same size and external character, such as balls of equal size but variously weighted. A spring instrument fitted with an index and a scale is also used. Where the extremities are

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thus tested it is necessary to so support them that no notion of the pressure be given by motions communicated to the joints and muscles.

The thermic sense can be quickly, though roughly, examined by first breathing and then blowing on a part. In order to estimate it more exactly it is best to use test-tubes filled with water at various known temperatures. Every test requires that considerable surface come in contact with the skin for a few moments, as the integument must gain or lose heat proportionately before the exact degree of temperature is appreciated. Within a few degrees of the ordinary body surface-temperature—namely, 80° to 86° F.-slight changes are not recognized in health./ Below this to freezing and above it to about 150° F. a variation of two to five degrees is readily perceived. Inability to recognize temperatures from 60° to 70° as cool and 86° to 100° as warm may be considered abnormal. Such a condition is denominated thermo-anesthesia, and, when complete, thermo-analgesia. Those parts of the skin possessing the most acute tactile sense are also most sensitive to heat. The term muscular sense is used in two ways:

First. It refers to the sensations arising in muscles themselves. In a painful degree this occurs in a cramp or in a tetanizing faradic contraction. The tension on muscles and tendons is no doubt subconsciously recognized by the coördinating mechanism, and it is only when these sensations are greatly intensified that we take conscious note of them.

Second. By muscular sense we refer to the ability to estimate the weight of various bodies. This ability is to so great an extent a result of practice and varies so widely among healthy persons that unless great differences of weight are not appreciated the test gives little information of value. Balls, such as those employed in the pressure test, can be used, or attempts made to repeat a fixed number on the dynamometer. When the sensation of tendons, joints, and muscles is blunted, not only is the muscular sense reduced, but knowledge of the position of the limbs is wholly or in part wanting and ataxia is present, as described under Errors of Motility.

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In certain conditions, notably tabes, sensation is retarded and the reaction time is greatly prolonged. A painful impression, as by the prick of a pin on the foot, may not be recognized and responded to for several seconds. In such cases the transmission of all touch sensations is slow. We prick the patient, having instructed him to say now as soon as he feels the needle, and note the interval, which, in health, is a small fraction of a second only. The intelligence and promptness of the patient materially affect the apparent length of intervening time. In some instances a single prick is recognized as two or more, or a painful impression is felt at a distant point,-a referred sensation,—or on the opposite side of the body at a symmetrical spot,-allocheiria.

Complete loss of sensation is properly termed anesthesia. Through usage this word signifies any degree of blunted sensation, and is qualified by adjectives such as partial, complete, or slight, as the case may require, and further limited by such combinations as muscle anesthesia, tactile, thermic, and joint anesthesia. The loss of the sense of pain is called analgesia, and this word is compounded in a similar way.

Sensation may also be intensified, giving rise to hyperesthesia and hyperalgesia. These conditions are made evident by the usual tests, and require no extended review.

In addition there are a host of purely subjective sensory disturbances, described as sensations of heat or cold, numbness, prickling, crawling, creeping, tingling, heaviness, deadness, etc.,-paresthesia. Areas so affected may show no alteration of sensibility when actually tested. Paresthesia usually are symptomatic of general nutritional states or of the so-called neuroses.

Having determined a localized dysesthesia, or condition of disturbed sensation, it is of the first diagnostic importance to outline it as accurately as possible. Sensation may be disturbed by lesions which involve sensory paths at any point from the cerebral cortex to the terminal organs in the muscles and skin. The dysesthesic area, however, presents a different and distinctive outline as various levels are injured.

If a nerve-trunk or branch be injured by traumatism or disease, anesthesia will be limited to the corresponding anatomical cutaneous distribution. Per contra, if such anatomical area be found to be anesthetic, the inference is at once justified that a peripheral lesion is present. As soon as the sensory nerve-fibers reach the spinal cord they ramify so widely in the various segments that it would be impossible for any spinal disease or injury to select a given number from all others. Figures 15 and 16 show these sensory areas, and should be carefully studied.

If the spinal cord undergo a complete cross-lesion or division, we have loss of sensation in the nerve-area below the upper level of the injury. Now, the distribution of anesthesia has relation to the cordsegments, and not to the nerve-trunks. For a practical understanding of this fact it is necessary to recall that the body, from one end of the vertebral chain to the other, is made up of a number of similar segments or links, all more or less perfectly represented in the skeleton, muscles, viscera, skin, and nervous apparatus. In the dorsal region the plan is comparatively simple, but as the limbs are reached it is greatly complicated. If vertical sections of the body were to be made approximately on these segmental lines, it would be requisite to place it in the all-fours position, making the coccygeal end of the vertebral column the posterior or last segment. The diagrams of Starr (Fig. 17) clearly show this, and the difference between the spinal-segment area and the nervetrunk representation of sensation is apparent. It at once becomes plain, when we find an anesthetic area corresponding to a spinal-segment level, that the lesion is in the cord and at a particular part of the cord; moreover, that its upper level corresponds to the upper level of the anesthetic zone. Just above this level, owing to the irritation of the sensory roots of the spinal nerves, there commonly is a band or girdle of hyperesthesia bordering the anesthetic area. This also serves to indicate the upper limit of the spinal lesion.

Should the cord injury involve only one lateral half of the transverse cord-section, the symptom complex of Brown-Séquard paralysis develops. The hemicordal lesion causes complete loss of power on the