SECT. V. PHYSIOLOGY. 31 
SECTION V. 
Muscular Irritability. 
tv. According to the opinion of Haller, irri- 
tability is an innate, peculiar, inherent property 
of muscular fibres; while he, at the same time, 
admits the influence which the vital force and 
volition exercise upon them. The doctrine having 
had most extensive credit with physiologists, I 
shall insert the author’s own words: “ Seperavi 
quidem irritabilem naturam hine a vi mortua, 
inde a vi nervosa, et ab anime potestate.” Whe- 
ther there be a foundation in nature for these nice 
distinctions of Haller, I am not to decide; but 
I shall confine myself chiefly to the consideration 
of the general effects produced on the muscles by 
variations of the vital force, both in health and 
disease. 
Lv. Lxpansibility of Muscles.—Moderate expan- 
sion is the natural quiescent state of the muscles; 
it is quite involuntary; or, at least, is effected 
without any effort of the mind, except when 
opposing muscles are employed to extend their 
antagonists with more speed, or to a greater than 
