30 PHYSIOLOGY. 



narcotics, which affect powerfully the nervous system; and even 

 electricity, which destroys muscular contractility, does not affect the 

 action of cilise. It continues much longer in cold-blooded than in 

 warm-blooded animals. The function of the cilise seems to be, to 

 propel the secretions, which would otherwise accumulate on these 

 membranes, towards the outlets. 



The epithelium cells, like the epidermic, are being constantly cast 

 off and renewed from the subjacent surface : but the rapidity of this 

 renewing process varies according to the particular function of the 

 part. 



OF THE COMPOUND MEMBRANO-FIBROUS TISSUES. 



This division includes the structures made up of the elementary 

 components of the body, viz. : membranes, fibres, and cells, in their 

 simplest forms. These are the serous, synovial, and mucous mem- 

 branes. 



The serous and synovial membranes are essentially alike in their 

 minute structure. On their free surface is a single layer of epithe- 

 hum, the particles of which are polygonal in shape, and of trans- 

 parent texture. This rests upon a continous transparent basement 

 memhrane of extreme tenuity. Beneath this is a layer of areolar 

 tissue^ which constitutes the chief thickness of the membrane, and 

 gives it its strength and elasticity. This areolar tissue is traversed by 

 a network of capillary vessels,, lymphatics, and nervous filaments in 

 varying number; and is the bond of union with the tissues beneath. 

 It is commonly known as the subse)'Ous tissue. 



The physical and vital properties of serous membranes are pre- 

 cisely those of areolar tissue. They are elastic, but not contractile, 

 and have very little sensibility, except when inflamed. They are 

 bedewed with a secretion which resembles the serum of the blood. 

 That of the synovial membranes and bursas mucosae has from 6 to 

 10 per cent of additional albumen. It escapes from the blood-ves- 

 sels by simple transudation. 



Serous membranes are recognised by the fact, that they always 

 form shut spcs. The peritoneum of the female is the only excep- 

 tion to this rule. At two points this membrane is open, where it 

 communicates with the canal of each Fallopian tube at its dilated 

 extremity. 



The mucous membranes may be said to consist of the three parts 

 described in the serous, viz. : epithelium^ basement membrane^ and 

 the subraucous areolar tissue. The mucous membrane is continuous 

 with the external skin, and by some is considered as identical. It is 

 recognised by the fact that it lines the outlets, and never occurs as a 

 shut sac. It is abundantly supplied with blood-vessels, absorbents, 

 and nerves. The first two are very numerous, the last not so much 

 so, hence the sensibility of this structure is usually low. 



The areolar tissue of mucous membranes usually makes up the 



