SECT. XV. PHYSIOLOGY. 123 
iris was renewed with that of the muscles. I have 
met with three cases besides, where the expansi- 
bility of the iris was affected in the same 
manner. On mature consideration of these cases, 
I cannot regard the cause of motion in the iris 
as different from the cause of irritability in the 
muscular and vascular systems. By the study 
of theories which multiply the agents of motion 
in the animal economy, the mind is bewildered, 
without being either amused or edified. 
-cexc. Sometimes the blood is so distributed in 
the brain, as to cause paralysis of some of the 
facial muscles; while the iris is only raised to 
its maximum of expansion. On the contrary, a 
slight excess of drinking occasionally brings on 
paralysis of the iris, without affecting any part of 
the muscular system. Cases of these descrip- 
tions are now and then to be met with in large 
hospitals. 
cexci. The motion of the iris is regarded by 
some physiologists, as voluntary in parrots; but, 
in all probability, their irises are affected by the 
nearness or distance of the objects on which they 
are looking; for even the human iris expands 
when the eye is directed to a near object, and 
contracts when regarding a distant one; but we 
do not say, on these accounts, that the motion of 
the human iris depends on volition. 
