SECT. III. PHYSIOLOGY. 23 
force; by which means I hope to explain some of 
the important functions of the animal economy, 
and arrive at a few conclusions of practical utility. 
xxxit. To avoid also any obscurity from arti- 
ficial technical classification, I shall distinguish 
the varieties of irritability by the anatomical de- 
nomination of the organs in which it exists. This 
arrangement is convenient in some respects, for 
though the vital force be the agent of motion in 
organized bodies, yet each organ is constructed 
to move by peculiar stimulants which only modify 
its vital force: light augments the action of the 
optic nerve, but is without influence on the 
olfactory and auditory nerves. 
