SEROUS MEMBRANES. 313 



found in France, and analyzed by Braconnot. He found it com- 

 posed of 



Silicious sand, . 4*0 



Gelatin, . .4-6 



Bitumen, . . 4'4 



Oxide of iron, . 0*5 



Alumina, . . 0*7 



Phosphate of magnesia, . 1 '0 

 Water, . . 1]-0 



Carbonate of lime, . 4*5 



Phosphate of lime, . 6 9 '3 



100-0 * 



CHAPTER XIX. 



OF SEROUS MEMBRANES. 



THE name serous membranes is applied to certain thin, pellu- 

 cid, and transparent tissues, which constitute shut sacs without 

 inlet or other interruption of continuity. They are called serous, 

 because they are constantly moistened by a thin albuminous 

 fluid, supposed to resemble the serum of blood. These serous 

 membranes in the human body are chiefly the following : 1. The 

 arachnoid membrane, which invests the brain, and which is pro- 

 longed over the spinal chord : 2. The two pleurce, which invest 

 the lungs; 3. The pericardium, which incloses the heart; 4. 

 The peritoneum, which is reflected over the different viscera of 

 the abdomen, together with the two processes which extend from 

 it upon the testes ; 5. The membrane which lines the anterior 

 chamber of the eye. Perhaps the lining coat of arteries and veins 

 may also be referred to the serous membranes. 



These membranes invest the viscera, which they inclose, and 

 are likewise reflected upon the walls of the cavity. It is the in- 

 vesting part of the serous membranes that gives to different or- 

 gans their shining appearance ; and as the membrane is very 

 thin and transparent, the colour, form, and even the minute in- 



* Gehlen's Jour, second series, iii. 49. 



