120 ANALYTIC SECT. XV. 
parallel straight lines, and the pupil resembles a 
small incision; but when the animal is carried 
to a dark place, the pupil resumes its circular 
shape. 
ccLxxxu. Another notion respecting the mo- 
tion of the iris is, that it expands in consequence of 
a more copious afflux of blood to it ; but how does 
this afflux happen? or do the fluids possess in 
themselves the slightest degree of moving power? 
and unless they have a self-moving force, it is 
impossible that they can move the iris in this 
ad libitum fashion. This theory is even more 
speculative than any that Haller has advanced on 
irritability. 
ccLxxxiul. It is however possible, that win 
exposure to a strong light may bring on expansion 
of the blood-vessels of the eye ; but in sucha case, 
the afflux of blood is the consequence, and not 
the cause of expansion. But if in an ordinary 
light any turgescence of the vessels of the iris did 
take place, what prevents its being observable in 
the cat, or in the almost diaphanous iris of the 
albino ? 
ccLxxxiv. Bichat admits frankly, that expan- 
sion of the iris precedes any afflux of blood to its 
vessels. “I have left out of this table,” says he, 
“the mode of motion of the iris and corpera caver- 
nosa, a motion which precedes the afflux of blood, 
and which is determined by it. I have left out, 
ee eee 
