VISION. 



819 



it has accommodation-reflex. It occurs in locomotor ataxia and in 

 paresis. Both pupils act, though only one retina is stimulated, owing 

 to the intercentral coupling of the two constricting centers of the 

 pupil. In dyspnoea the pupil dilates, but when asphyxia ensues the 

 dilatation diminishes. Atropine paralyzes the oculomotorius terminals 

 (thus paralyzing accommodation), but after its section the dilatation 

 of the pupil is still further increased by atropine; hence it must be 

 an action on the dilating fibers. Eserin, a myotic, contracts the 

 pupil, due to stimulation of the oculomotor. The anaesthetics con- 

 tract the pupil, but when their action is deep they dilate it. 



WERNICKE'S HEMIOPIA PUPILLARY BEACTION. If the light is 

 thrown on the hemianopic half of the retina, the pupil remains inac- 

 tive. Here there is an interruption in the path between the retina 

 and the geniculate bodies; the hemiopia is not central, but due to 

 a lesion in the tract of the optic nerve. If the light is thrown on 

 the sensitive half of the retina, the pupil immediately contracts. 



