SYSTEMATIC SYNTHESIS OF TISSUES INTO ORGANS. 305 



819. THE FLUID FURNISHED TO THE EYE contains an 

 appreciable quantity of salt to render it transparent. 

 When this is not supplied the eye soon inflames ; in such 

 cases, to wash it frequently with a solution of salt in 

 water will be highly serviceable. Too much salt in the 

 blood, and in the tear-fluid, on the other hand, tends to 

 inflame the eye. 



Protections of the Eyes. 



820. THE PROTECTIONS OF THE EYE are the lids, 

 the Meibomian glands, the orbicularis muscle, the lashes 

 that fringe the lids, and the eyebrows that shed off the 

 perspiratipn and catch particles of dust that might in- 

 commode the eyes. 



821. Remark. WHEN DUST DOES ENTER THE EYE, one of the best 

 ways of removing it is to draw the upper lid down over the lower lid, 

 and let it slide up. This experiment is almost always successful, and 

 particularly valuable on the cars. 



Review of the Eye. 



822. A REVIEW OF THE EYE SHOWS that perfect vis- 

 ion depends upon a very large supply of Blood to its 

 nervous part, to sustain the great activity of the retina ; 

 upon a proper form and density of the Media of the eye; 

 and upon the reception of a proper supply of light; 

 while incidentally the front surface must be kept moist 

 and protected from dust. 



823. THE EYE MUST HAVE repose, temporarily as 

 well as at long intervals. 



824. Illus. If the eye be acted upon continuously by any color, in 

 a short time the object of regard will begin to appear dark, on account 

 of the exhaustion of the eye, no longer able to respond to the light. If 

 then another color be presented to the eye, it will be discerned with 

 great pleasure ; if it be white, the complementary part of it only will be 

 effective. For example, if the eye regard red till fatigued, and look 

 upon white, it will see green, that is, the blue and yellow of white. 



819. What said of ? 820. What are ? 821. What to be done ? 822. What 

 does - ? 823. What must ? 824. Illustrate the idea. 



