: ... C ^30 ] 
lows, according to the degree of that impreflion : in 
the cafe of diftant objects, the faint impreffions of 
light on the retina make the pupil contract little, 
and it remains wide; for dilatation is the natural 
Hate of the pupil. In obferving very near objects, 
the light is cceteris panbus Hronger, and ftimulates 
the retina , and contracts the pupil more. 
In a word, the contractions of the uvea arife from 
the fenfations of the retina involuntarily and uniform- 
ly, according to an invariable law and connexion; 
otherwife why does the pupil conftantly become 
immoveable, when -by a gutta ferena the retina be- 
comes inlenfible ? Let any one obferve the motions 
of the pupil, by the help of a mirror, they will al- 
ways find it impracticable to fubjeCt them to the 
will. Indeed it is clear from experiments, as well 
as difeafes, that the iris , like all other parts provided 
with nerves from ganglia , has but a dull degree of 
feeling, and is moved entirely independent of the 
will*. << What perfuades me, fays M. de Haller, 
“ that the iris is much lefs fenfible than the retina, 
is, that if, after having pierced the cornea , you ir- 
“ ritate or cut the ins , it is not therefore contracted, 
“ whereas the lead increafe of light makes it con- 
“ traCt ; which evidently proves that this contraction 
“ d°5 s not depend upon the proper fenfibility of the 
“ ins, but on that of the retina . The gutta ferena 
ferves to prove the fame thing, the iris being no 
<l ways changed in that difeafe, any further than it 
“ deprived of motion, from the fenfation of the 
“ tetina , being deftroyed by a palfy of the optic 
“ nerve. Lffay on Irritability, p. 31. 
* See Why tt, EfT. on the Invol. motions. Le Cat, on the Scn- 
fes. Haller, Elem. Phyf, kc. 
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