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MANUAL OF PHYSIOLOGY. 



The cells produce in their protoplasm a quantity of the secretion, 

 which may often be seen to swell them out to a considerable 

 extent. This clear fluid is then expelled, and the altered cells 

 are repaired or replaced. Many elements, like the remains of 

 epithelial cells, are found in the secretion ; and also round nu- 

 cleated masses of protoplasm similar to white blood corpuscles, 

 after the imbibition of water. In the abnormal secretion of a 

 mucous surface during inflammation these mucous corpuscles 



FIG. 165. 



Section of the Mucous Membrane of upper part of nasal cavity, showing 

 numerous Mucous Glands cut in various directions. a, Surface epithelium ; 

 b, gland saccule; c, connective tissue lined with secreting cells. (Cadiat.) 



are, as well as the general amount of secretion, enormously in- 

 creased, so that the secretion may become opaque, and may appear 

 to be purulent. 



The chief object of the secretion seems to be to protect the mu- 

 cous surfaces, which are rich in delicate nerves and vessels, and 

 are subjected to many injurious influences of a chemical or me- 

 chanical nature. It is analogous to the keratin of the epidermis, 

 and may be regarded as an excretion, since it is not absorbed, but 



