SOME LESSONS ON THE HUMAN BODY 1 1 



their transparency. Circular musular fibres in the iris 

 by their contraction allow less light to enter the eyeball, 

 and as they relax the pupil of the eye is enlarged. Dust and 

 any foreign particles lodged underneath the eyelids, or an 

 irritation due to lack of tear-water, may cause congestion 

 of the blood vessels in the eyeball and in its surroundings. 

 This gives the eye a temporary blood-shot appearance. 



Pain in the eyes as elsewhere in the body is nature's warn- 

 ing that something is wrong with the mechanism. Weariness 

 is a signal for rest, or a demand that an abuse of the eyes 

 be stopped. Rest for the eyes when reading, sewing, 



A ' 



FIG. 3. Formation of images on the retina of the eyeball. (So far 

 as the physics of the phenomenon is concerned the images thus formed are 

 inverted.) 



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or using the microscope, does not necessitate complete dis- 

 use of the eyes. Any occupation that requires sustained 

 effort to see the same object, especially if dimly lit up, soon 

 wearies the eyes. Looking at other objects at different 

 distances rests the eyes. The little muscles that hold the 

 lens of the eye in a particular form in order to see any ob- 

 ject distinctly are often kept under a strain which not only 

 wearies but weakens them. The effect is somewhat the same 

 as when one forces himself to hold his arm out horizontally 

 from the body for a long time. Any serious ailment of the 

 eyes calls for their examination and possible treatment. 

 Glasses fitted by oculists, while commonly for the purpose of 



