SPASM (from the Creek erratra6s) is an unhealthy, involuntary, and forcible contraction of muscular tissue. The term is almost syno nymous with convulsion, but is more generally applied than that word is to the unhealthy painful contractions of the heart, intestines, and other involuntary muscles.
Nosologists have distinguished spasms into clonic, in which the muscular contractions alternate rapidly with relaxations (as in epilepsy), and tonic, in which the contracted fibres remain for a long time rigid, BS in tetanus; but in nature the distinction is not well marked. Spasm has also often been regarded as occurring in many tissues in which it is perhaps not possible, such as the small blood-vessels. In the present day its occurrence is believed to be limited to the muscles. What their condition is when affected by spasm is not precisely known. Very generally the contraction is unnatural, not only in its origin and its continuance, but in its extent ; for it does not take place simulta neously, or in a regular succession, in each part of the muscle, but, as one may often see in common cramp, it affects a single portion of the muscle, drawing it up into a hard mass, while the fibres above and below it are much less contracted, or are even elongated.
The greater number of spasms seem to depend on an irritation of the nervous centres. Sometimes they are produced by primary disease in those parts, but much more commonly they are the results of irritation propagated from some disordered organ to the brain or spinal cord, and thence reflected through the motor nerves of the muscles in which the spasm occurs. Hence probably the frequency and the aggravation of cramps, and other more important spasmodic affections, when the digestive organs are disordered, the dependence of a variety of spasms or convulsions on the irritation of teething, Site. Much less, however, is known of the nature of spasm in general than of the best methods of treating it, and of the effects which it produces in the several organs which it affects. These are treated of in the articles ANGINA PECTORIS; ANTISPASMODICS; ASTHMA ; COLIC; ColsvtrLsioNs; EPILEPSY ; HYDROPHOBIA ; TETANUS, &C.