512 THE EYE. 



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

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

 up into a colloid state. The 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 laminse. 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, in transparent 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 w r ater, 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 



