ANIMAL ORGANIZATION. 101 



ment of parts is resisted by their elasticity, but, 

 when displaced, they tend to return to their 

 natural position. This property performs a 

 more important part in the mechanism of the 

 animal than of the vegetable system ; as might, 

 indeed, have been anticipated from the more 

 active and energetic movements required by the 

 functions of the former. 



The cellular texture, in its simple form, admits 

 of the ready transmission of fluids through it ; 

 but it is necessary, on many occasions, to inter- 

 pose a barrier to their passage. Such barriers 

 are provided in membranes, which are merely 

 modifications of the same material, spread out 

 into a continuous sheet of a closer texture, after 

 the surfaces of the plates have been brought to 

 cohere so as to obliterate all the cellular in- 

 terstices, and become impervious to fluids. 

 Though equally flexible and elastic with the ori- 

 ginal texture of which it is formed, the mem- 

 brane has acquired, by this consolidation, greater 

 strength and firmness, properties which adapt 

 it to a great number of important purposes.* 



Membranes are extensively employed to con- 

 nect distant organs, and often serve to determine 

 the direction and extent of their relative motions. 



* With a view of ascertaining the actual strength of mem- 

 branes, Scarpa stretched a portion of peritoneum, (which is a very 

 thin membrane lining the abdominal cavity), over a hoop, and 

 placing weights upon its surface, found it did not give way till it 

 was loaded with fifteen pounds. 



