84 PHYSIOLOGY. 



often to be increased by causes which weaken their vigour ; and y 

 therefore, it is induced by the diminution of tension, and by 

 causes weakening the animal, nervous, or inherent powers. 

 " Mobility is evidently more remarkable in weaker bodies ; as 

 in children, in women, in persons weakened by various means, 

 such as a diminution of tension, and other causes affecting the 

 animal power." 



CVIII. The ordinary contraction of muscular fibres is dis- 

 posed spontaneously to alternate with a relaxation or extension 

 of the same. 



CIX. In the straight muscles, and in the heart, the alter- 

 nate contractions and relaxations readily take place ; and that 

 though a stimulus is constantly applied ; but in muscular fibres 

 surrounding cavities, as in the alimentary canal, bladder of 

 urine, &c. the alternate motions do not appear, unless a portion 

 of the fibres is cut out and separated from the rest 



CX. From a difference in the state of a muscle contracted 

 by inherent power, while the member it sustains is moved by 

 external force, and that of the same muscle contracted by the 

 power of the will, we perceive that in the muscles there may be 

 a state of relaxation without their extension. " The experi- 

 ment is that which I mentioned (CIV.) with regard to the 

 biceps muscle." 



CXI. There is a state of the contraction of muscles that is 

 not disposed spontaneously to alternate with relaxation, and in 

 which too the fibres do not easily yield to extending powers ap- 

 plied. Such a state of contraction is called a SPASM. " There 

 is not a term now more frequent in our Pathology than that of 

 spasm; it is as old as any writings in physic, and has been on 

 many occasions employed with very different meanings, so that 

 it is necessary to limit its sense. As the word was originally 

 used to express contraction in general, every kind of contrac- 

 tion might be called a spasm or drawing together; but it is 

 necessary to have different terms to express the different modi- 

 fications or states of contraction. Where pathologists have 

 used the term according to the ancient meaning, they have dis- 

 tinguished the spasmi into tonici and clonici : this, in my 

 opinion, is more difficult language than that of spasm and con- 

 vulsion, which last, taken generally, comprehends every other 



