4o DISEASES Class I. i. 4. 1. 



ORDO I. 



Increafed Irritation, 



GENUS IV. 



With increafed Actions of other Cavities and Membranes. 



SPECIES, 



t. Niclitatic irritaiiva. Winking of the eyes is performed 

 every minute without our attention, for the purpofe of cleaning 

 and moiftening the eye-ball \ as further fpoken of in Clafs II. 1. 

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

 time lefs tranfparent ; 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 palling through it ; in the fame 

 manner as light is refra£ted by palling near the edge of a knife. 

 When thefe pores are filled with water, the cornea becomes, 

 again tranfparent. This want of tranfparency of the cornea is 

 ■vifible fometimes in dying people, owing to their inirritability, 

 and confequent neglect of nictitation. 



The increafe of tranfparency by filling the pores with fluid is 

 feen by foaking white paper in oil 5 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 diftant objects lefs diftinct, it is a fign of a dry day ; 

 when diftant objects are (ecu very diftinct, 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 pal's 

 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 pafiing through them. But when as much moif- 

 ture is added as can be perfectly diiTolved, 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 furnmer-days, or over 

 brick-kilns, after the ilanie is extinguifhed, while the furnace 

 flill remains hot. 



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

 formed frequently without our attentionjandis then an irritative 

 acticTi hi confequence of the ftimulus of it in the mouth. Or 



perhaps 



