( 2^8 ) 



" the manner of an onion, or other bulbous root, include its humours, 

 " by which name are uiiclerftood three lubltances, tlie one a folid. the 

 '• other a foi't body, and the third truly a liquor. Thefe fubftances 

 " are of fuch forms and tranlparcncy, as not only to tranfmit rea- 

 " diJy the rays of light, biit alfo to give them the polition bell 

 " adapted for the purpofes of viiion. They are clear like water, and 

 " do not tinge the objeit with any particular colour. 



" Aqueous Hutnour. 



" T\\Q moft fluid of the three humours is called the aqueous one ; 

 " filling the great interface between the cornea and the pupil, and 

 *' alfo the fmall fpace extending from the uvea to the cryilalline lens ; 

 " it is thin and cle;a- like water, though fomewhat more fpiritous and 

 " vifcuous ; its quantity is fo confiderable, that it fwells out the fore 

 " part of the eye into a protuberance very favourable to vifion. The 

 " uvea fwims in this fluid. It covers the fore part of the cryftalline; 

 " that part of this humour which lies before the uvea, communicates 

 " with that which is behind, by the hole which forms the pupil of 

 " the eye. It is included in a membrane, fo tender, that it cannot 

 '• be made vifible, nor preferved, without tiic moft concentrated lixi- 

 " vial fluid. 



" It has n.ot been clearly afcertained whence this humour is derived ; 

 *' but its fource muft be plentiful : for if the coat containing it be fo 

 " wounded, that all the humour runs out, and the eye be kept clofed 

 " for a feafon, the wound will heal, and the fluid be recruited. 



'* The colour and confiflence of this humour alters with age ; it 

 " becomes thicker, cloudy, and lefs tranfparent, as we advance in 

 " years, which isoncrcafon, among others, why many elderly peo- 

 " pie do not reap all that benefit from fpedacles which they migh 

 ♦' .naturally expert 



