512 THE EYE. 



nitrogenized body (mucin). It does not appear to be 

 dissolved in tbe water of tbe mucus, but to be swollen 

 up into a colloid state. Tbe liquid contains, besides 

 this, potassium and sodium chlorides, and small quan- 

 tities of other salts. Mucus is not coagulated by heat- 

 ing, but precipitated by alcohol and dilute acetic acid. 



13. Transudates of Serous Membranes. 



The fluid, which collects in dropsical affections, con- 

 tains albumen in varying, frequently in very large 

 quantity ; and, in addition to this, the ordinary salts 

 and undetermined substances. It is usually alkaline. 

 Occasionally it contains urea and cholesterin sus- 

 pended in fine laminae. The amniotic fluid and the 

 fluid in hydatids contain the same ingredients. When 

 boiled or treated with nitric acid, these fluids become 

 more or less turbid or coagulated. 



Pus is a creamy, thick, intransparent liquid, which 

 consists of a clear, colorless, or slightly yellow serum 

 (pus-serum), and, suspended in this, the pus-corpuscles 

 and fat-globules. Pus-serum contains albumen, which 

 coagulates by heat, and further,- leucine, sodium chlo- 

 ride, and other inorganic salts. Pus-corpuscles possess 

 the greatest resemblance to the colorless blood-cor- 

 puscles. 



14. The Eye. 



The sclerotic, formed of very compactly interwoven 

 cartilaginous fibres, can, like the corium, be dissolved 

 as gelatin, by long-continued boiling with water. 



The cornea is formed of a peculiar tissue, and con- 

 ducts itself chemically like chondrigenous cartilage, 

 but swells up in acetic acid. 



The black pigment (melanin), which is deposited in 

 the form of microscopical, brown granules in separate, 

 closed cells in the choroid, is insoluble in water, alco- 

 hol, and dilute acids; soluble in potassa, forming a 

 dark-yellow liquid ; is reprecipitated by acids. It con- 

 tains 13-14 per cent of nitrogen. When subjected to 



