A convulsion-, or involuntary contraction of the muscles, (from convello, to pu/l together). Called also hieranosos, distensio nervorum.

Dr. Cullen places this genus of disease in the class neuroses, and order spasmi; and defines it, "an irregular clonic contraction of the muscles without sleep,"of which he enumerates nine idiopathic species; and five symptomatic. See Nosologiae Methodicae Synopsis, p. 216, vol. iii.

Under the spasmi Dr. Cullen includes the tonic and the clonic spasms, where the muscles are rigidly and immovably contracted; and where the violent, irregular contractions are alternated with equally sudden relaxations. This arrangement is formed with the strictest propriety, as we shall afterwards find.

Convulsions attack persons of all ages, but chiefly the young, or the debilitated; all constitutions, but principally the fair, the delicate, and the irritable; each sex, but particularly females. Its causes are various; but the chief source of convulsions is, in the opinion of every author, irritation. It is certainly irritation, in systems peculiarly mobile, in other words, easily excited to action; but, as the mobility is greater, the irritation necessary to produce convulsions is less; and sometimes so slight as to be imperceptible.

If we examine the functions of the nervous system, we shall find life and health depend on the regular distribution of the nervous power. If it is hurried, irregularly exerted, or deficient, various diseases, and particularly convulsive ones,ensue. Joy, grief, surprise, will equally produce them. Violent exertions, and tone, suddenly relaxed, are also causes of these irregular motions. We do not find, however, that with high health, full vessels, and a firm constitution, however the circulation is accelerated, or the nervous power excited, convulsions ensue, unless the tone is suddenly remitted. Whatever effect therefore may be attributed to predisposition, the causes are chiefly debilitating ones; and the constitutions chiefly affected, those which are weak. It is then irregular action, in weak habits, which constitutes the disease. In palsies of every kind, tremors attend every exertion; and the various species of tremor in Sauvages', one only excepted, are obviously from debility. In hysteria there is usually considerable debility, though the circulating system is often full; and indeed there is no more common cause of weakness than over distended vessels. This is the exception noticed in Sauvages' species of tremor. In epilepsy this debility is less obvious, but the most obstinate cases occur in weak constitutions; and, in others, the irregular action is excited by peculiar and violent stimuli, chiefly affecting the organic structure of some part of the nervous system. The palpitations in chlorosis, the gesticulations in chorea, the convulsive agitations in raphania, the causes of true convulsive asthma, all confirm the idea, that debility is the cause of irregular action. Nor need we add, for it is the subject of common observation, that convulsions close the scene, particularly of disorders induced by excessive evacuations and worn out constitutions; that they are effects of narcotics of every kind, of deleterious gases, mineral exhalations, and even of stimulants that exhaust the vital power, and increase, inconsequence, the irritability. We may therefore rest safely on the position, that irregular action, either spasmodic or clonic, has its foundation in debility or in irritability; but the former is most frequent, as it is a very common cause of increased mobility.

From the effects of narcotics, of deleterious gases and similar powers, we have reason to conclude, that irregular action may arise from debility alone, or at least from obscure and unperceived irritation. Yet in practice we must always keep in view the existence of irritation; and we often find it necessary to check this exciting, at the risk of increasing the power of the predisposing, cause. There is little doubt, for instance, that the irritation of the meconium sometimes produces the locked jaw and convulsions in new born infants; this must be evacuated. The sedative power of lead produces the Poitou colic: this irritation must be soothed by opium before laxatives will succeed. A wounded nerve will occasion a locked jaw; the irritation on the nerve must be removed by destroying its sensibility, and the increased action of the muscles at the same time counteracted by appropriate remedies, general and topical. Other convulsions are more effectually remedied by warm stimulants and tonics: the warmest stimulants are often required in the convulsions from sedative poisons or the deleterious gases. In this short disquisition, our first object was to establish the principle, that convulsions are rather irregular than increased action, and that their primary cause was debility: our second, not to mislead the young practitioner, who, by attempting to counteract debility, may lose sight of the exciting cause, irritation.

How debility acts in producing convulsions we pretend not to say, nor is the inquiry of importance; there seems, however, to be a ruling power in the constitution, which regulates the distribution of the nervous influence; and, when it is weakened, this influence is irregularly distributed. We mean not to say, with Stahlians, that this power is all wise, and directs every thing for the general good; exciting these convulsions to throw off some noxious matter, threatening destruction to the whole system. If such a power exists, it is implanted by the Almighty; regulated according to his fiat by secondary causes; and acting necessarily from the organisation of the machine. In another view, the whole nervous influence may be regulated by its state in the brain; and, if that arrangement is altered by any violently stimulant or sedative impression, the rest must suffer a similar change: and, when we contemplate the various phenomena which diseases of the nervous system present, we are rather inclined to adopt this opinion. We have, however, already observed that our object is to establish principles, not to build systems.