(_f_) The various internal organs, the viscera, supplied with striped or unstriped muscular fibres, may be paralyzed. (_g_) The muscular coat of the vascular system beyond the heart may be paralyzed in extensive or limited areas—the so-called vaso-motor paralysis. This may assume hemiplegic or monoplegic or localized forms. SPASM, or HYPERKINESIS, consists in abnormal and often violent involuntary muscular contractions, with or without loss of consciousness. 1. A purely mechanical classification of spasms into tonic and clonic forms is generally admitted as serviceable for clinical description, though we have as yet no positive knowledge of their relations to pathological conditions. (_a_) Tonic or tetanic spasm is one in which the muscular contraction is continuous or constant for a measurable length of time. Thus, in some cases of petit mal there is a momentary stiffness or rigidity of the entire {45} voluntary muscular apparatus (respiratory muscles included): the patient sits or stands with staring eyes as if petrified. In tetanus and local tetanoid seizures the muscles of large regions or of a part of a limb may remain contracted for many minutes; in the disease called tetany this condition may endure days and weeks—in hysteria and in some paralyses dependent upon organic disease for years or permanently. Prolonged tonic spasms occurring in chronic diseases are designated as contractures, and the affected parts are said to be tetanoid or spastic. A tonic spasm of long duration may show itself in involuntary muscles, as in the arteries, causing vaso-motor spasm and ischæmia; in the ciliary muscle, causing spasm of accommodation; in the urethra, œsophagus, etc. A tonic muscular contraction accompanied by intramuscular pain is termed cramp. Under this general head may also be classed the emotional or dramatic expressive spasms of hysteria and hystero-epilepsy—a condition in which the emotions or ideas occurring in the patient's mind are involuntarily translated externally into attitudes or gestures: _e.g._ anger, fear, disgust, amorous and religious feelings, etc. (_b_) Clonic spasms are those which consist in rapidly intermittent muscular contractions, local or general. These may be rhythmical in time or form, as in paralysis agitans, or wholly irregular, as in chorea. Jerking is a quasi-popular designation of clonic spasms.