Spasm (Gr. spasma) consists in an irregular and violent contraction of muscular parts—involuntary even when the voluntary muscles are concerned. There are two sorts of spasm. In one there is an unusually prolonged and strong muscular contraction, not rapidly alternating as usual with relaxation, the relaxation only taking place slowly, and after some time. This is known as tonic spasm (Gr. tonos, 'a bracing up') or Cramp (q.v.). When in a more moderate degree affecting the voluntary muscles generally it constitutes Catalepsy (q.v.), in which, from the muscles remaining contracted, the limbs will retain whatsoever attitude they are placed in, until the spasm is over. But the extreme example is Tetanus (q.v.), in which the spasms are so violent and so enduring that they may be said to squeeze the patient to death. In the other form of spasm the contractions of the affected muscles take place repeatedly, forcibly, and in quick succession; the relaxations being, of course, equally sudden and frequent. This is named clonic spasm (Gr. klonos, 'an agitation'), and is popularly known as convulsions. The spasmodic twitches which sometimes occur in the muscles that close the eyelids (orbicularis palpebrarum) are familiar to almost everybody, and are an example of clonic spasm on a very small scale. Epilepsy and convulsive hysteria afford the best examples of this kind of spasm. Chorea (q.v.), or St Vitus's dance, is an allied but less regular and characteristic form.
The treatment varies according to the cause of the excessive muscular irritability. Firm pressure on muscles affected with spasm will promote their relaxation, and by strong steady pressure on the masseter muscles the lower jaw has been depressed, so as to open the mouth, in cases of lock-jaw. The medicines which are employed to counteract irregular or inordinate muscular action are termed antispasmodics; but spasm may depend upon so many different causes that the remedies which are found most successful in combating it must vary extremely in their nature. There are, however, a few medicines which appear to exercise a control over spasmodic action generally. These may be termed pure or true antispasmodics. They are Asafœtida, Cotyledon umbilicus (or Common Navel-wort), Wood-soot, Galbanum, Musk, Rue, Sagapenum, Sumbul (Jatamansi or Musk Root), and Valerian and the Bromides. Amongst the narcotics often useful in these affections we may especially mention Belladonna, Cannabis Indica (or Indian hemp), Chloral, Opium, and Stramonium. Sulphuric ether in draught or inhaled, and inhaled chloroform, are often of service. In some cases, remedies which directly depress the vital powers, such as the prolonged use of the warm bath, or even, in rare cases, the abstraction of blood, are the most effectual means of subduing spasm.