=Incoördination= (_Dyskinesis_) is the lack of the harmonious balanced movement of the various groups of muscles. Coördination of movement is due to a special mechanism in the spinal cord, and extending forward through the medulla oblongata, pons, and crura cerebri to the floor of the third ventricle. In the form of _ataxia_ (lack of power of muscular control) it is usually the result of degeneration (sclerosis) of the superior columns of the cord, of the medulla, pons or crura. It may occur from degeneration or destructive change in the cerebellum, or from disease or section of the posterior roots of spinal nerves, or finally from the action of certain narcotic poisons (ptomaines, toxins). =Staggering= (_titubation_) occurs from lesions of the cerebellum, medulla or pons; also from alcohol, opium, and other narcotics. =Reflex Action.= The normal stimulation of different functions, motor, secretory, circulatory, etc., depends on the nerve centres in the spinal cord, which are roused into action by a centripetal impulse derived from a distant part. Thus the balanced contraction of the different muscles which preserves the equilibrium of the body, depends on the apprehension by the nerve centres, consciously or subconsciously, of such contractions (muscular sense), and it is largely under the control of the will. Here three impulses act coördinately: 1st, the afferent impulse from the muscle to the nerve centre; 2d, the efferent impulse from the nerve centre to the muscle; and 3d, the inhibitory or controlling, voluntary impulse from the sensorium to the nerve centre involved. In another case, savory odors, sapid flavors and masticatory movements cause a free secretion from the salivary glands. Again, the scratching of a dog’s breast causes him to move his hind limb as if he were himself doing the scratching. Again, the pricking of a limb causes the prompt, even if involuntary, contraction of its muscles to withdraw it from the source of irritation. =Morbid Reflex.= Reflex action may be modified in various ways as the result of disease or injury. It may become excessive from irritability of the organ from which the centripetal impulse starts, or of the reflex centre in the spinal cord, or of the muscle or other organ to which the centrifugal impulse is directed, or, finally, from impairment of, or separation from the inhibitory centre in the cerebrum. It may be impaired or abolished from degeneration or destruction of any of the tissues just named, or of the conducting nerves which connect them to each other. The contraction and closure of the pupil under light is a reflex act from the retina on the optic lobes, etc., and from these through the motor oculi to the iris. This reflex is lost and the iris fails to contract in: anæsthesia of the retina; atrophy of the optic nerve; disease of the optic lobe; superior (posterior) spinal sclerosis; disease of the motor oculi; or disease of the iris.