40 , DISEASES CLASS I. i. 4. i, 



O&DO I. 



Increafed Irritation. 



GENUS IV. 



With Increafed Actions of other Cavities and Membranes. 

 SPECIES. 



1. Niflitatio irritativa. Winking of the eyes is performed 

 every minute without our attention, for the purpofe of cleaning 

 and moiftening the eye-ball j as further fpoken of in Clafs II. i . 

 I. 8. When the cornea becomes too dry, it becomes at the fame 

 time lefs tranfparent j which is owing to the pores of it being 

 then too large, fo that the particles of light are refracted by the 

 edges of each pore, inftead of pafling through it ; in the fame 

 manner as light is refracted by pafling near the edge of a knife. 

 When thefe pores are rilled with water, the cornea becomes 

 again tranfparent. This want of transparency of the cornea is 

 vifible fometimes in dying people, owing to their inirritability, 

 and confequent negledft of nictitation. 



The increafe of tranfparency by filling the pores with fluid is 

 feen by foaking white paper in oil ; which from an opaque body 

 becomes very tranfparent, and accounts for a curious atmofpher- 

 ic phenomenon ; when there exifts a dry milt in a morning fo as 

 to render diflant objects lefs diftincl:, it is a fign of a dry day ; 

 when diftant objecls are feen very diftin6t,, it is a fign of rain. 

 See Botan. Garden, Part I, add. note xxv. The particles of air 

 are probably larger than thofe of water, as water will pafs 

 through leather and paper, which will confine air, hence when 

 the atmofphere is much deprived of moifture, the pores of the 

 dry air are fo large, that the rays of light are refracted by their 

 edges inftead of pafling through them. But when as much moif- 

 ture is added as can be perfectly diflblved, the air becomes tranf- 

 parent \ and opaque again, when a part of this moifture collects 

 into fmall fpherules previous to its precipitation. This alfo ac- 

 counts for the want of tranfparency of the air, which is feen in 

 tremulous motions over corn-fields on hot fummer-days, or over 

 brick-kilns, afref the flame is extinguilhed, while the furnace 

 itill remains hot. 



2. Deglutitio irritativa. The deglutition of our faliva is per- 

 formed frequently without our attention, and is then an irritative 

 aclion in confequence of the ftimulus of it in the mouth. Or 



perhaps 



