122 ANALYTIC SECT. XV. 
particular stimulants; thus, the optic nerve is 
susceptible of having its action augmented by the 
rays of light. 
ccLxxxvil. Nothing can be simpler than trying 
the irritability of the iris: expose the pupil to a 
strong light, the fibres of the iris that instant 
expand, and the diameter of the pupil is lessened; 
reduce the quantity of light, their length is dimi- 
nished, and the pupil enlarged. The iris thus 
follows the same general law as the skin and 
muscular fibres, augmentation of the vital force 
producing expansion, and diminution of it, con- 
traction. 
ccLxxxvu. When there is an afflux of blood 
to the brain, it sometimes occurs that the action 
of the optie nerve is raised to a great height; and 
in all such cases, the expansion of the iris cor- 
responds with the intensity of the vital force. 
But if the afflux of blood be so great as to dimi- 
nish the action of the brain by compression, or 
by whatever mode it acts, and produces paralysis, 
the optic nerve is sometimes compressed, and the 
iris becomes also paralyzed, and the pupil is 
preternaturally large. : 
- CCLXxxIx. Dilatation of the pupil of one eye is 
thus frequently a symptom of hemiplegia; but it 
is not confined to the side opposite to the one 
paralyzed. The case of Deschamp shows, that 
by raising the vital force, the expansibility of the 
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