LIQUID PARTS OF ANIMALS. 



water and a little empyreumatic oil is driven off. The residue 

 consists of common salt mixed with some soda and small quanti- 

 ties of the phosphates. 



Alcohol precipitates white flocks from tears. These flocks were 

 considered by Fourcroy and Vauquelin as constituting a species 

 of mucus. This mucus, they say, has the property of absorbing 

 oxygen from the atmosphere, and of becoming thick and viscid, 

 and of a yellow colour. It is then insoluble in water, and re- 

 mains long suspended in it without alteration. When chlorine 

 is added to tears, a yellow flocky precipitate falls, possessing the 

 same properties as inspissated mucus. This property of the mu- 

 cus of tears enables us to understand the alterations which that 

 liquid undergoes when long exposed to the action of the atmo- 

 sphere, as is the case with those persons who labour under ajis- 

 tula lachrymalis. 



The substances found in tears by Fourcroy and Vauquelin 

 are the following : 



Water. Soda. 



Mucus. Phosphate of lime. 



Common salt. Phosphate of soda. 



CHAPTER XVII. 



OF THE LIQUORS OF THE EYE. 



THE globe of the eye consists of several coats inclosing with- 

 in them three different humours. The one farthest back, and 

 constituting a considerable portion of the eye-ball, is called the 

 vitreous humour. It is a transparent and colourless liquid inclos- 

 ed in a great number of cells. Between the cornea and the lens 

 of the eye, there is another colourless and transparent liquid cal- 

 led the aqueous humour; and the crystalline lens, though not li- 

 quid but solid, has got the improper name of the crystalline hu- 

 mour of the eyes. 



The first attempt to examine these three humours, and to deter- 

 mine their chemical constitution, was made by Mr Chenevix in 

 1802.* He made his experiments on the eyes of sheep and oxen, 

 and made some observations also on the humours of the human 



* Phil. Trans. 1803, p. 195. 



