33$ APPLIED PHYSIOLOGY 



at now will show a colored spot shaped like the first object, 

 for a part of the retina is no longer able to recognize all 

 the colors which make white light. Its color will always 

 be complementary to the color of the object first looked at. 

 Thus when a red object is used first, a green image ap- 

 pears. The eye is really made color blind for a brief 

 period. 



Ordinary lamps and gas jets give a yellowish light, while the sunlight 

 is white. So by lamp light, the colors of objects seem to be changed. 

 In incandescent electric lamps the light is given off from a white-hot 

 filament. Owing to its steadiness, its color and the absence of heat 

 and foul gases, it is the most agreeable light in common use. 



613. Care Of the eyes. No light should be strong enough to 

 dazzle the eyes. When, as in public halls, bright lights are in front of 

 the eyes, there is a natural tendency to gaze directly at them, thereby 

 tiring the retina. It would be better to look at the darkest objects in 

 the room. 



It is best to have the light come from behind the eye. In working 

 with a lamp in front of the eyes, a shade should cover either the light 

 or the eyes. When the sun shines brightly upon the snow the excess 

 of light exhausts the retina. Then the eyes become painful, and blind- 

 ness may result. 



614. Contraction of the pupil. A strong light excites 

 the reflex center in the optic tubercles to send out an 

 order for the contraction of the muscles of the iris so as 

 to make the pupil smaller. On the other hand, in the 

 dark the pupil is large, so as to admit all the light possi- 

 ble. When a light is very strong, the reflex centers send 

 orders to the muscles both of the upper and lower lids, 

 and of the eyebrows to pucker themselves over the eyes, 

 so as to leave only a narrow slit for the entrance of light. 

 In this way the eyes are well protected against too strong 

 lights, but the contracted muscles may become tired and 

 painful. 



