SECT. VI, PHYSIOLOGY. 37 
SECTION VI, 
Contractibility of Muscles. 
ux1x. The vital force has hitherto been con- 
sidered as a simple substance, arising from the 
combined operation of the nerves and blood-ves- 
sels, as a power generating heat, and expanding 
the muscular fibres. These preliminary propo- 
sitions being established, what is the cause of 
muscular contractibility ? The muscles themselves 
being the production of the vital force, it must, 
I conceive, necessarily follow, that they derive 
their faculty of contracting from the same source. 
Taking this for granted, it remains to be shown, 
what are the modifications of the vital force 
which cause the opposite states of muscular ex- 
pansion and contraction. The subject may be 
taken in two points of view; the first is the 
opinion of Hoffman, who seems to have consi- 
dered morbid muscular contraction as simply 
caused by reduction of the vital force; the latter 
is to regard the vital force as a compound sub- 
stance. Hoffman’s theory is the most useful one 
that has ever been advanced, but it is not appli- 
