TEARS. 511 



When heated over a spirit lamp it dries, swells a little, and is char- 

 red, and burning with a small flame. When digested in ether, 

 a little fatty matter is dissolved, to which the flame was doubt- 

 less owing. When examined by the microscope, it appears com- 

 posed of irregular transparent plates, mostly colourless, though 

 sometimes yellowish. When globules appear in it the mucus is 

 probably partially converted into pus. The diameter of these 

 globules varies from I? ^th to T ^ 5 th of an inch. 



CHAPTER XVI. 



OF TEARS. 



THE fluid which is employed in lubricating the eye, and which 

 is emitted in considerable quantity, when we express grief by 

 weeping, is known by the name of tears. It is secreted by the 

 lachrymal gland, a conglomerate gland about three-quarters of 

 an inch in length, and half an inch in breadth, situated in the 

 upper and outer part of the orbit. No attempt has been made 

 to make a chemical examination of the tears, since the experi- 

 ments of Fourcroy and Vauquelin in 1791.* 



The liquid, called tears, is transparent and colourless like 

 water. It has no perceptible smell, but its taste is sensibly sa- 

 line. Its specific gravity has not been determined, though it is 

 known to be heavier than distilled water. It tinges syrup of 

 violets green, and of course contains a free alkali. It may be 

 mixed with water in all proportions. Alkalies unite with it rea- 

 dily, and render it more fluid. The mineral acids do not sensi- 

 bly alter it. When exposed to the air, it gradually evaporates 

 and becomes thicker. About the end of the evaporation a num- 

 ber of cubic crystals of common salt make their appearance. 

 They give a green tinge to vegetable blues, and therefore con- 

 tain; an excess of alkali. The mucous animal matter of tears ac- 

 quires a yellow colour as it dries. Tears boil like water, except- 

 ing that a considerable froth collects on the surface. When boil- 

 ed to dryness over the steam-bath, tears lose 96 per cent, of 

 their weight, which flies off in the state of water. The remain- 

 ing 4 parts have a yellowish colour. When strongly heated, 



* Jour, de Phys. xxxix. 254. 



