fj(3 PHYSIOLOGY. 



of contraction, which is attended with a degree of rigidity ; and 

 the impetus of the blood in the vessels overstretching their 

 fibres, leaves them in the same state. But I will not touch this 

 subject further, as I cannot explain what is the state of spasm 

 strictly so called ; but it leads us to this, that as there is a state 

 of increased mobility, so a state of diminished mobility takes 

 place to a morbid degree in our nervous fluid. Thus, in 

 chronic rheumatism, and after strains and spasms, not only do 

 the muscular fibres remain in a preternaturally rigid state, but 

 we find the nervous fluid in them is now not moveable by the 

 animal power, so that we cannot exert the further contraction, 

 which the animal power is otherwise capable of doing." 



CXI I. When muscles are excited to contraction by preter- 

 natural causes, and are contracted with unusual velocity and 

 force, and especially when the contractions, alternating with re- 

 laxation, are frequently and preternaturally repeated, such mo- 

 tions are called CONVULSIONS. 



" The causes of spasm and convulsion may be referred to three 

 heads : 1. Whatever disturbs the ordinary measure and order in 

 the exertions of the animal power I say, that in all men custom 

 has established a measure in the velocity and force of every ac- 

 tion, and an order in every series of actions ; this has a certain 

 latitude, which is different in different men, and in different ac- 

 tions, but in every man that latitude has its limits; and if the mind 

 is urged beyond that established limit of velocity and order, it 

 commonly loses its measure, and readily runs to the degree of con- 

 vulsion and spasm ; this is sufficiently evident with regard to par- 

 ticular muscles : thus I am frequently liable to spasm, and the 

 cause is some degree of strain in the motion I excite. If I turn 

 about short and more quickly than ordinary, I have the whole of 

 that side of the shoulder and thorax affected with spasm ; and 

 in most violent exertions we readily throw the muscles into 

 spasms. But still it is more remarkable with regard to the exer- 

 tions of the animal power in the brain ; there, all hurry in the 

 emotion or passion does produce a general effort of epilepsy, 

 and hence the effects of surprise. All strong impressions which 

 are sudden, throw moveable systems into convulsion and 

 spasm, or into delirium or irregularity in the motions of 

 the animal power. An illustration, which, I think, is very 



