THE SPECIAL SENSES. 43 



the eye. This is called the lachrymal or tear gland. 

 It secretes from the blood a watery fluid which it 

 pours out upon the eyeball. By the act of winking 

 the eyeball is entirely bathed by this fluid, which 

 after it has flowed over the eye, collects in a little 

 lake at the inner angle, from whence it is drained by 

 two little channels (2) into the tear duct (1) which 

 communicates with the nose. Shedding tears is 

 simply an overflow of this eye-bathing fluid, when 

 it is secreted in unusual quantity. At such times 

 the little channels cannot carry it away sufficiently 

 rapid; so it flows over upon the cheeks. This unu- 

 sual activity of the tear gland may be produced by 

 certain states of the mind, as sorrow or great joy; 

 or by certain diseased conditions of the parts about 

 the eye, as an inflammation or a severe cold. 



The eyeball has three coats. The outer 



The wVhite 



Coat of the coat, or white of the eye, is called the 

 Eyeball. sclerotic. It is a strong, tough mem- 



brane which forms quite a substantial case into 

 which the cornea is set in front, like the glass or 

 crystal of a watch. The sclerotic coat is not sensi- 

 tive ; that is, it has no nerves of feeling. But it is 

 covered, in front, with a very delicate membrane 

 which contains very fine blood-vessels and nerves. 

 When these little blood-vessels become swollen with 

 an unusual amount of blood, the eye is said to be 

 "bloodshot;" and when a cinder or dust grain 

 lodges on the eye and makes an impression on the 

 delicate nerves of this fine protecting veil, the sen- 



