SYSTEMATIC SYNTHESIS OF TISSUES. 193 



202. THE SEKOUS MEMBRANE is like the preceding, 

 except that it is thinner, and has but a single layer of 

 thin cells forming its surface, pouring out a watery fluid 

 called serum. It is called by many different names in 

 different places, though always one thing ; for example, 

 Pleura, at the surface of the Lungs, Peritoneum, in the 

 Abdomen, Dura- Mater, when lining the Skull, &c. 



203. THE LATTER TWO COMPOUND MEMBRANES enter 

 into the composition of a large number of organs ; and 

 though they are compound parts, they are usually con- 

 sidered and spoken of as elements of organs. As they 

 are common to many, it is proper that they should be 

 briefly described under the head of General Physiology. 



SECTION IX. 



Liquids. 



204. THE CHIEF PART OF ATT. THE LIQUIDS IN THE 

 BODY is FORMED of Water, which, in fact, is the liquid 

 of the Body, having more or less of various substances 

 dissolved in it. 



205. WATER SERVES FOUR PURPOSES IN THE BODY : 

 1st, as a vehicle it transports the substances dissolved 

 in it, and also heat, from place to place ; 2d, it moistens 

 the soft solids of the Body, in fact, makes them soft and 

 pliable for when it is dried away they become hard ; 3d, 

 by evaporating from the Skin and Lungs it removes a 

 corresponding amount of heat ; 4th, when removed from 

 the circulation by the Kidneys, the quantity of Blood 

 is correspondingly diminished, passes round the quicker, 

 produces more heat in a given time, circulates it faster, <fcc. 



206. WATER is merely a chemical compound ; serves 

 simply mechanical purposes in the Body, and is intro- 

 duced and used by physical means alone. 



802. What - ? What its special names ? 203. What said - ? 204 Of what ? 

 206. How does ? 206. What ? 



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