LIGHT AND LIFE. 133 



this spontaneous movement of the infant's eyes is thwarted, 

 strabismus may be the consequence. 



Of all our organs the eye is the one that light especially 

 affects. Through the eyes come all direct notions of tke 

 outer world, and all impressions of an aesthetic kind. Now, 

 the excitability of the retina shows variations of every 

 kind. Prisoners confined in dark cells have been known to 

 acquire the power of seeing distinctly in them, while their 

 eyes also become sensitive to the slightest changes in the 

 intensity of light. In 1766 Lavoisier, in studying certain 

 questions upon the lighting of Paris, which had been given 

 for competition by the Academy of Sciences, found, after 

 several attempts, that his sight wanted the necessary sensi- 

 tiveness for observing the relative intensities of the differ- 

 ent flames he wished to compare. He had a room hung 

 with black, and shut himself up in it for six weeks in utter 

 darkness. At the end of that time his sensitiveness of 

 sight was such that he could distinguish the faintest differ- 

 ences. It is very dangerous, too, to pass suddenly from a 

 dark place into a strong flood of light. The tyrant Diony- 

 sius had a building made with bright, whitewashed walls, 

 and would order wretches, after long seclusion from light, 

 to be suddenly brought into it. The contrast struck them 

 blind. Xenophon relates that many Greek soldiers lost 

 their sight from reflections off the snow in crossing the 

 mountains of Armenia. All travelers who have visited 

 the polar regions have often seen like results produced by 

 the glare of the snow. When the impression of light on 

 the eye is sudden and overpowering, the retina suffers 

 most. If it is less powerful, but longer continued, the 

 humors of the eye are affected. The phenomenon called 

 sunstroke results from the action of light, and not, as is 

 often supposed, from excessively high temperature. It 

 sometimes occurs in the moderately warm season of spring ; 

 or a very intense artificial light, and particularly the elec- 



