40 DISEASES CLASS I. 1. 4. 1. 



ORDO I. 



Increased Irritation. 



GENUS IV. 

 Wilh increased fictions of other Cavities and Membranes. 



SPECIES. 



1. Nictitatio irritativa. Winking of the eyes is performed 

 every minute without our attention, for the purpose of cleaning 

 and moistening the eye-ball; as further spoken of in Class II. 1. 

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

 time less transparent; which is owing to the pores of it being 

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

 edges of each pore, instead of* passing through it; in the same 

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

 When these pores are filled with water, the cornea becomes 

 again transparent. This want of transparency of the cornea is 

 visible sometimes in dying people, owing to their inirritability, 

 and consequent neglect of nictitation. 



The increase of transparency by filling the pores with fluid is 

 seen by soaking white paper in oil; which from an opaque body 

 becomes very transparent, and accounts for a curious atmosphe- 

 ric phenomenon; when there exists a dry mist in a morning so as 

 to render distant objects less distinct, it is a sign of a dry day; 

 when distant objects are seen very distinct it is a sign of rain. 

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

 are probably larger than those of water, as water will pass 

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

 the atmosphere is much deprived of moisture, the pores of the 

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

 edges instead of passing through them. But when as much mois- 

 ture is added as can be perfectly dissolved, the air becomes trans- 

 parent; and opaque again, when a part of this moisture collects 

 into small spherules previous to its precipitation. This also ac- 

 counts for the want of transparency of the air, which is seen in 

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

 brick-kilns, after the flame is extinguished, while the furnace 

 remains hot. 



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

 formed frequently without our attention, and is then an irritative 

 action in consequence of the stimulus of it in the mouth. Or 



